The first model of the atom was developed by JJ Thomson in 1904, who thought that atoms were composed purely of negatively charged electrons. This model was known as the 'plum pudding' model
Final answer:
Scientific theories and models change over time due to new evidence and experimentation, leading to more accurate predictions and descriptions of natural phenomena. The dynamic nature of science, such as in phylogenetic modeling in biology, necessitates continual revision and refinement of theories. This iterative process propels scientific discovery and understanding.
Explanation:
Why Theories and Models Change Over Time
The development of scientific theories and models is an iterative process, continually influenced by new data and experiments. As scientists observe nature more meticulously, they gather evidence that may either corroborate or challenge existing theories. The predictive ability of models plays a crucial role in their validity; precise models enable accurate descriptions and predictions about natural phenomena. For instance, Albert Einstein's general theory of relativity radically improved our understanding of gravity, leading to predictions and the eventual discovery of black holes.
In fields like biology, the concepts of phylogenetic modeling have undergone significant change. Scientists propose new models as new research provides insights into the relationships between organisms, showcasing the dynamic nature of scientific study. Ultimately, a theory must withstand rigorous testing, and when new evidence warrants, theories are refined or replaced to incorporate this newfound understanding.
The pathway from data to scientific discovery is often directed by the models, theories, and laws that scientists construct. These not only assist in analyzing collected data, but also guide researchers to novel discoveries, furthering the cycle of scientific progress.
Each Thursday the 11 kindergarten students in Miss Goodson's class are each allowed one slice of pie, one cup of orange juice, and two doughnut holes. The leftovers will be given to the custodian on the night shift.
How many slices of pie are left for the custodian?
slices of pie
How many cups of orange juice are left for the custodian?
cups of orange juice
How many doughnut holes are left for the custodian?
donut holes
How many were there to start off with?
The custodian receives 5 slices of pie, 7 cups of orange juice, and 11 doughnut holes as leftovers.
To calculate the leftovers for the custodian, we must first calculate how many items the students consume and subtract that from the total provided by the caterer:
Pies: There are 2 pies, each cut into 8 slices, for a total of 16 slices. With 11 students, 11 slices will be used, leaving 5 slices for the custodian.Orange juice: There are 18 cups of orange juice and each of the 11 students gets one cup, leaving 7 cups for the custodian.Doughnut holes: There are 33 doughnut holes. Each student eats 2 doughnut holes, so 11 students will consume a total of 22 holes, leaving 11 doughnut holes for the custodian.When solutions of silver nitrate, AgNO3, and calcium iodide, CaI2, are mixed, a yellow precipitate of silver iodide is formed. Calculate the mass of silver iodide that is formed if 50.00 mL of 1.00 M AgNO3 is combined with 30.00 mL of 1.25 M CaI2.
Answer:
[tex]\boxed{\text{11.7 g}}[/tex]
Explanation:
We are given the amounts of two reactant solutions, so this is a limiting reactant problem.
We know that we will need a balanced equation with masses, moles, and molar masses, so, let's assemble our information in one place, with molar masses above the formulas and the
M_r: 234.77
2AgNO₃ + CaI₂ ⟶ 2AgI + Ca(NO₃)₂
Solution: (50.00 mL, 1.00 M) (30.00 mL, 1.25 M)
Step 1. Calculate the moles of each reactant
Moles of AgNO₃ = 50.00 mL × (1.00 mmol/1 mL) = 50.00 mmol
Moles of CaI₂ = 30.00 mL × (1.25 mmol/1 mL) = 37.50 mmol
Step 2. Identify the limiting reactant
Calculate the moles of AgI we can obtain from each reactant.
From AgNO₃:
The molar ratio of AgI:AgNO₃ is 2:2.
Moles of AgI = 50.00 mmol AgNO₃ × (2 mmol AgI/2 mmol AgNO₃)
= 50.00 mmol AgI
From CaI₂:
The molar ratio of AgI:CaI₂ is 2:1.
Moles of CaI₂ = 37.50 mmol × (2 mmol AgI/1 mmol CaI₂) = 75.00 mmol AgI
AgNO₃ is the limiting reactant because it gives the smaller amount of AgI.
Step 3. Calculate the mass of AgI.
Mass = 50.00 mmol AgI × (234.77 mg AgI /1 mmol AgI)
= 11 700 mg AgI = 11.7 g AgI
The mass of silver iodide formed is [tex]\boxed{\textbf{11.7 g}}[/tex].
What are some ways that you can limit your use of greenhouse gases? explain.
If people are to drive less it only means fewer carbon dioxide emissions because people will save on gasoline. Similarly, it helps keep around 20 pounds of carbon dioxide out of this atmosphere thus reducing the amount of greenhouse gases. Clearly, car related emissions are the major cause of global warming.
Change a light. Replacing one regular light bulb with a compact fluorescent light bulb will save 150 pounds of carbon dioxide a year.
Recycling helps reduce greenhouse gas emissions by reducing energy consumption. Using recycled materials to make new products reduces the need for virgin materials. This avoids greenhouse gas emissions that would result from extracting or mining virgin materials.
The energy in fossil fuels is often converted into
Answer: The energy in fossil fuels is often converted into Electrical Energy or more simply, electricity
The energy in fossil fuels is often converted into different forms of energy, such as thermal, mechanical and electrical energy. This is most commonly achieved through burning fossil fuels, which releases thermal energy that can be used to drive steam engines or to generate electricity.
Explanation:
The energy in fossil fuels is often converted into several other forms of energy, most notably heat or thermal energy. This conversion of energy from one form into another happens all the time. For example, when fossil fuels such as coal, petroleum or natural gas are burned, the chemical energy they contain is converted into thermal energy. This thermal energy can then be used to heat buildings or to operate steam-driven machinery which then converts the thermal energy into mechanical energy. In electric power plants, this mechanical energy is further converted into electrical energy by rotating coils of wire in magnetic fields to generate electricity. It is important to note that not all of the initial energy is converted into the forms mentioned, as some energy is always transferred to the environment.
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Need help !!!!! ASAP
The answer is:
The temperature will be the same, 37°C.
Why?Since from the statemet we know the first temperature, pressure and volumen of a gas, and we need to calculate the new temperature after the pressure and the volume changed, we need to use the Combined Gas Law.
The Combined Gas Law establishes a relationship between the temperature, the pressure and the volume of an ideal gas using Boyle's Law, Gay-Lussac's Law and Charles's Law.
The law establishes the following equation:
[tex]\frac{P_{1}V{1}}{T_{1}}=\frac{P_{2}V{2}}{T_{2}}[/tex]
Where,
[tex]P_{1}[/tex] is the first pressure.
[tex]V_{1}[/tex] is the first volume.
[tex]T_{1}[/tex] is the first temperature.
[tex]P_{2}[/tex] is the second pressure.
[tex]V_{2}[/tex] is the second volume.
[tex]T_{2}[/tex] is the second temperature.
Then, we are given the following information:
[tex]V_{1}=200mL\\P_{1}=4atm\\T_{1}=37\°C\\V_{2}=400mL\\P_{2}=2atm[/tex]
So, isolating the new temperature and substituting the given information, we have:
[tex]\frac{P_{1}V{1}}{T_{1}}=\frac{P_{2}V{2}}{T_{2}}\\\\T_{2}=P_{2}V{2}*\frac{T_{1}}{P_{1}V_{1}} \\\\T_{2}=2atm*400mL*\frac{37\°C}{4atm*200mL}=37\°C[/tex]
Hence, we have that the temperature will not change because both pressure and volume decreased and increased proportionally, creating the same relationship that we had before the experiment started.
The temperature will be the same, 37°C
Have a nice day!
What does ethylene glycol do to the solution in a vehicle’s radiator? It raises the boiling point and lowers the freezing point. It lowers the boiling point and lowers the freezing point. It lowers the boiling point and raises the freezing point. It raises the boiling point and raises the freezing point.
Answer:
It raises the boiling point and lowers the freezing point.
Explanation:
It is used as antifreeze in the cooling circuits of internal combustion engines, that is, it is used to reduce the melting point of the solution.
By adding ethylene glycol I'm not only bringing the melting point to -13°C, but the boiling point of ethylene glycol is 197°C.
since these substances not only lower the freezing point but also increase the boiling point, they are also called a colligative agent
Answer:
The correct option is A) It raises the boiling point and lowers the freezing point.
Explanation:
Consider the provided information.
Ethylene glycol is often used for convective heat transfer.
The freezing point of pure ethylene glycol is about −12° C and boils at 198° C.
Due to the higher boiling point and antifreeze properties, it is used in a vehicle’s radiator.
Therefore, the correct option is A) It raises the boiling point and lowers the freezing point.
A rocket with its thruster on is speeding up towards the Moon. Therefore, what type of force is acting on the rocket? A. zero net force B. frictional force C. balanced force D. unbalanced force
Answer:
[tex]\boxed{\text{D. Unbalanced force}}[/tex]
Explanation:
If a rocket is at rest or moving at a constant velocity, the forces on it are balanced.
If the engines are ignited in flight, the thrust from the propellant gases unbalances the forces, and the rocket speeds up.
A is wrong. There can't be zero net force if the rocket is accelerating.
B is wrong. There is no friction in space.
C is wrong. The forces can't be balanced if the rocket is accelerating.
The weight of an object never changes.
True
False
the answer to your question is
true
Answer: False depending on what you do or what happens to the object but true if nothing happens to it
Explanation:
Sharing electrons between atoms indicates an ionic bond.
A. True
B. False
The sharing electrons between atoms indicates an ionic bond is FALSE.
I hope this helps
The sharing of electrons between atoms indicates an ionic bond is option B. False.
Why does the sharing of electrons between atoms indicate an ionic bond is False?Ionic bonding is presented as the complete transfer of valence electrons, typically from a metal to a non-metal.In reality, electron density remains shared between the constituent atoms, meaning all bonds have some covalent character.The ionic or covalent nature of a bond is determined by the relative electronegativities of the atoms involved.The bond that involves the sharing of electron pairs between atoms is that what kind of atoms form covalent bonds with nonmetals why do metals not form covalent bonds they don't hold onto their electrons well.Hence, the sharing of electrons between atoms indicates an ionic bond is False.
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Which of the following sources of pollution would be the most difficult to track and regulate? a. lawn fertilizer runoff b. a waste treatment plant c. a factory d. a nuclear power plant Please select the best answer from the choices provided A B C D
a. lawn fertilizer runoff
Pollution as a result of lawn fertilizer runoff would be difficult to track and regulate due to the possible breadth of the area affected. Toxins can be spread throughout the land area as well as be carried downstream if near a water source. Sewer systems, rivers, lakes, ponds, etc. can all be negatively affected by lawn fertilizer runoff. Irrigation or rain water can carry toxins for many miles before the effects are detected. Tracing the source of the toxins would be difficult, especially in a highly populated area.
Lawn fertilizer runoff is a source of pollution that would be difficult to track and regulate as compared to others.
Why lawn fertilizer is difficult to track and regulate?Pollution that occurs as a result of lawn fertilizer runoff would be difficult to track and regulate because of the large size of the area. Toxins present chemical fertilizer can be spread throughout the land as well as also added to the water source.
So that's why we can say that Lawn fertilizer runoff would be more difficult to track and regulate as compared to others.
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what happens to sodium sulphate in water
Answer:
It dissolves into the water
Na₂SO₄ + H₂O → 2Na₊_{aq} + SO₄²-_{aq}
Hope this helps :)
Have a great day !
5INGH
Explanation:
2
Which two traits best help a cactus conserve water in the dry conditions of a West
Texas desert ecosystem?
Answer: Sharp spines and waxy stems
Sharp spines because it keeps predators away and it’s skin helps keep in water
Oil is a natural resource that is found inside of Earth. Oil can be used
Answer:
ti make gas to make things work and for stalk on the market
Explanation:
At 98.66 kPa and 20 degrees C nitrogen has a solubility in water of .018 g/L. At 82.66 kPa and 20 degrees C, it’s solubility is .015 g/L. Does nitrogen obey the gas pressure-solubility law?
Yes it’s corrrct I swear
At 98.66 kPa and 20°C nitrogen has a solubility in water of .018 g/L. At 82.66 kPa and 20°C, it’s solubility is 015 g/L. Nitrogen obey the gas pressure solubility law.
What is Henry Law ?Henry's Law is a gas law states that the solubility of a gas in liquid is directly proportional to the pressure of that gas.
It is expressed as:
[tex]P_{i} = K_{H}\ X_{i}[/tex]
where,
[tex]P_{i}[/tex] = Partial pressure of the gas
[tex]X_{i}[/tex] = Mole fraction of gas
[tex]K_{H}[/tex] = Henry's Law constant
Which will not obey Henry Law ?Ammonia, Hydrogen halide (like Hydrochloric acid) and Hydrogen sulfide these gases does not obey Henry's Law.
Thus from the above conclusion we can say that At 98.66 kPa and 20°C nitrogen has a solubility in water of .018 g/L. At 82.66 kPa and 20°C, it’s solubility is 015 g/L. Nitrogen obey the gas pressure solubility law.
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elements in the same period have the same ___________?
Answer:
number of energy levels
Explanation:
for example hydrogen and helium are in period 1 and they have 1 energy level
Which best describes why a liquid needs a container when a solid does not?
liquid is fluid in motion, needing to be contained. while a solid state of matter is as such and won't run down the cabinet
Answer:
When an element or substance is in a liquid state, the particles are joined by less attractive forces than in solids, for this reason the particles of a liquid can move freely.For this reason the particles of a liquid can move freely and need a recipient that contains them .
Liquids have a defined volume but with a variable shape, this means that liquids adopt the shape of the container but always occupy the same space
For example, if we have 4 L of water in a round container, its shape is round and now we put the water in a square container, its shape is now square but its volume is still 4 L (it continues to occupy the same space)
What would the charge be on an ion of boron (B)?
Answer:
3+
Explanation:
Boron belongs to the 3rd group, the Boron family on the periodic table. It has an atomic number of 5. For neutral atoms of Boron, we have 5 electrons in them.
All atoms lose or gain electrons in order to achieve a perfect noble gas configuration which would give them stability. Noble gases are known to be stable and unreactive.
For Boron, it would readily want to lose 3 electrons so as to mimic a Helium, He atom. Helium is the first element in the noble gas series.
When Boron loses 3 electrons, a net charge of 3+ is left on the atom of Boron.
Which sources are reliable? Check all that apply.
A.an article discussing mineral resources written by the United States Geological Survey
B.a blog discussing sources of alternate energy written by a high school student
an advertisement for guided hikes and tours in Camping magazine
C.a study describing clinical trials of a new medication in the Journal of Medicinal Chemistry
D.an entry about common uses of metals in an encyclopedia that can be edited by the general public
Answer:
It is options A and D.
Explanation:
Did the assignment.
Final answer:
The reliable sources from the given options are the article by the United States Geological Survey and the study published in the Journal of Medicinal Chemistry, both of which are credible due to their authoritative and scholarly quality.
Explanation:
Among the given options, the following sources are considered reliable:
An article discussing mineral resources written by the United States Geological Survey (USGS), which is a government publication or agency website that provides credible and factual information.A study describing clinical trials of a new medication in the Journal of Medicinal Chemistry, which is a peer-reviewed academic publication containing work that has been evaluated by experts in the field.Reliable sources are essential for research and credible, trustworthy, and unbiased information. These sources guarantee that the evidence and facts presented support the conclusions drawn. The USGS is a reputable government agency known for its research and the publication of scholarly articles, making it a credible source. The Journal of Medicinal Chemistry is part of the peer-reviewed academic publications, which are often published by academic institutions or associations, ensuring a rigorous process of review that adds to their credibility.
Some sources, such as a blog by a non-expert or a publicly editable encyclopedia, lack authoritative oversight and therefore are not as trustworthy. To ensure credibility, consulting multiple reliable sources is recommended, and sources like reputable newspapers, magazines, academic journals, and government publications are generally reliable.
Which characteristics do Jupiter and Saturn share? Check all that apply
They are mostly made of gas
They have few moons
They are the same size as earth
They have rings
They have thick atmospheres
Answer:
The correct answers are first, fourth, fifth
Explanation:
The characteristics that Jupiter and Saturn share include the following:
They are mostly made of gasThey have ringsThey have thick atmospheresIt should be noted that Jupiter and Saturn are known to be the two largest planets. They are also composed of two main elements which are helium and hydrogen.
Also, Saturn has 8 rings while Jupiter has 4 rings. Saturn and Jupiter are mostly made of gases and have thick atmospheres.
In conclusion, the correct options are 1, 4, and 5.
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Why is the blood that flows from the heart bright red rather than dark red?
Answer:
The oxygen-rich blood is then pumped out to your body through your arteries. It's bright red at this point. ... Your lips have a lot of these capillaries, which is why they're red. Your blood, now exhausted of its oxygen, is dark red as it now returns to your heart through your veins.
Explanation:
Answer:
The bright red blood leaving your heart is that color because it has more oxygen. The blood loses some oxygen and turns darker red before it returns to your heart.
Explanation:
What is the value of n in CH3(CH2)nCH3 if the name of the hydrocarbon is heptane
Answer:
n = 5.
Explanation:
How many carbon atoms in total in this straight-chain hydrocarbon?
The prefix of the IUPAC name of a hydrocarbon (the part before -ane) shows the number of carbon atoms on the longest carbon chain.
[tex]\begin{array}{c|c}\text{Number of Carbon}\\ \text{atoms in backbone} & \text{Prefix}\\[-0.5em]\multicolumn{2}{c}{\rule{5cm}{0.5pt}}\\1& \text{meth-} \\ 2&\text{eth-} \\ 3&\text{prop-}\\4 & \text{but-}\\5 & \text{pent-} \\ 6 & \text{hex-} \\ 7 & \text{hept-} \\8 & \text{oct-}\\ \dots & \dots\end{array}[/tex].
Name of this hydrocarbon: heptane;Prefix: hept-;Number of carbon atoms in the longest chain: 7.Hence the structure:
[tex]\text{CH}_3\text{-CH}_2\text{-CH}_2\text{-CH}_2\text{-CH}_2\text{-CH}_2\text{-CH}_3[/tex].
All the [tex]\text{-CH}_2\text{-}[/tex] in the formula might look redundant. "[tex]\text{CH}_2[/tex]" appears five times in a row and may be condensed into [tex](\text{CH}_2)_5[/tex]. Hence the condensed formula:
[tex]\text{CH}_3\text{-}{(\text{CH}_2)_{\bf5}\text{-CH}_3[/tex].
Therefore [tex]n = 5[/tex].
Answer:
n+5 so the correct answer is b) 5
Explanation:
just did review on edge
how many grams are in 5.2 moles of Li2SO4
Answer:
572 g
Explanation:
Molar mass is the mass of 1 mol of an element or compound
molar mass of Li₂SO₄ is the sum of the products of the molar masses of the elements by the number of atoms in the compound
molar masses of each element making up lithium sulphate
Li - 7 g/mol
S - 32 g/mol
O - 16 g/mol
molar mass of Li₂SO₄ - (7 g/mol x 2) + ( 32 g/mol x 1) + ( 16 g/mol x 4 )
molar mass = 110 g/mol
mass of 1 mol of Li₂SO₄ is 110 g
therefore mass of 5.2 mol of Li₂SO₄ is - 110 g/mol x 5.2 mol = 572 g
mass is 572 g
Given this reaction, N2O4(g) 2NO2(g), what shifts will occur if Q = K?
A.
the reaction shifts to the left
B.
the reaction shifts to the right
C.
no shift as the reaction is in equilibrium
D.
no shift because the product is 2NO2
Answer:
C. No shift as the reaction is in equilibrium
Explanation:
Q (the reaction quotient) and K (the equilibrium constant are equal) which means it's in equilibrium.
Atoms,which are always neutral in electric charge, contain electrons as well as protons and neutrons. An electron has an electrical charge of -1. If an atom has three electrons, infer how many protons it has.
Answer:
3
Explanation:
Since the atom has three electrons, it has a -3 electrical charge. Since atoms are neutral, 3 protons are needed to get the charge back to 0.
An atom maintains a neutral charge when it has an equal number of protons and electrons. Therefore, an atom with three electrons will have three protons. This principle is integral to the formation of ions when atoms gain or lose electrons.
Explanation:An atom is characterized by having an equal number of protons and electrons, thus maintaining a neutral charge. Protons carry a positive charge and electrons a negative one. Keeping in mind that a neutral atom has an equal number of both, if an atom has three electrons, it also has three protons.
In Chemistry, we know that atoms are neutral if they contain the same number of positively charged protons and negatively charged electrons. When the counts of these particles are unequal, the atom is electrostatically charged and is called an ion. This charge is calculated as: Atomic charge = number of protons - number of electrons.
For instance, if a neutral sodium atom (Z = 11) with 11 electrons loses one, it forms a cation with a 1+ charge (11 - 10 = 1+). Conversely, a neutral oxygen atom (Z = 8) gaining two electrons becomes an anion with a 2- charge (8 - 10 = 2-).
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Calculate the molar mass of aluminum nitride
The formula of aluminum nitride is AlN
the molar mass of Al = 27 amu
the molar mass of N = 14
(1 x 27) + (1 x 14)
= 27 + 14
= 41 amu
2zn+o2=2zno
how many moles of zinc are needed to make 6 moles of zinc oxide?
Answer:
[tex]\boxed{\text{6 mol}}[/tex]
Explanation:
(a) Balanced equation
2Zn + O₂ ⟶ 2ZnO
(b). Calculation
You want to convert moles of ZnO to moles of Zn
The molar ratio is 2 mol Zn:2 mol ZnO
[tex]\text{Moles of Zn} =\text{6 mol ZnO} \times \dfrac{\text{2 mol Zn}}{\text{2 mol ZnO}} = \text{6 mol Zn}\\\\\text{You need }\boxed{\textbf{6 mol of Zn}}\text{ to form 6 mol of ZnO}.[/tex]
To make 6 moles of zinc oxide, you would need 6 moles of zinc based on the balanced chemical equation 2Zn + O2 → 2ZnO.
Identify the balanced chemical equation: 2Zn + O2 → 2ZnOFrom the equation, 2 moles of Zn are needed to produce 2 moles of ZnO.Therefore, to make 6 moles of ZnO, you would need 6 moles of Zn.
HELP ASAP!
An ice cube has _____ than a cup of hot tea.
A)less heat energy
B)more cold energy
C)more heat energy
D)less cold energy
Final answer:
An ice cube has less heat energy than a cup of hot tea because the particles in the ice cube have lower kinetic energy than those in hot tea. The term 'cold energy' is not scientifically accurate; heat energy transfer is the correct concept. The correct answer is A) less heat energy.
Explanation:
An ice cube has less heat energy than a cup of hot tea. This statement aligns with the behavior of heat energy where the particles of a colder substance, like an ice cube, move much slower and thus have lesser kinetic energy compared to the particles in a warmer substance, such as hot tea. Therefore, the correct answer is A) less heat energy. The concept of 'cold energy' is not a scientific term in physics; instead, we discuss energy transfer in terms of heat. For instance, when an ice cube melts, it absorbs heat energy from its surroundings. Hence, a cup of hot tea has more heat energy, which is why it can transfer energy to the ice cube causing it to melt.
What is the possible reason for Trial B not obeying the law of conservation of mass?
A) Too much vinegar was used.
B) The reaction happened too fast.
C) Not enough baking soda was used.
D) The balloon-like device was not used in this trial.
I believe the answer is D. The ballon-like device was not used in this trial.
I am very sorry if this is not what you meant.
Apply A hydrate contains 0.050 mol of H,O for every
0.00998 mol of ionic compound. Write a generalized
formula of the hydrate.
Answer:
General formula of the hydrate XY.5H₂O
Explanation:
The general formula of a hydrate is given by; XY.nH₂O
Where n is the number of water of crystallization;
n = Moles of H₂O/Moles of XY
= 0.050 Mol/0.00998 moL
= 5.01
≈ 5
Therefore, the generalized formula of the hydrate is XY.5H₂O
Describe the difference between chemical and physical weathering
Difference Between Chemical and Physical Weathering.
Weathering processes crack, wear away, and weaken rocks.
While physical weathering breaks down a rock's physical structure, chemical weathering alters a rock's chemical composition.
Final answer:
Physical weathering is the process of breaking down rocks without changing their chemical composition, while chemical weathering involves chemical reactions that alter the composition of rocks. Physical weathering can occur through forces like freeze-thaw cycles, while chemical weathering can happen through processes like oxidation and hydration.
Explanation:
Physical weathering, also known as mechanical weathering, is the process of breaking down rocks and minerals into smaller pieces without changing their chemical composition. This occurs through physical forces such as freeze-thaw cycles, temperature changes, abrasion, and pressure.
Chemical weathering is the process in which rocks and minerals are broken down by chemical reactions that alter their composition. This can happen through processes such as oxidation, hydration, hydrolysis, and carbonation. Chemical weathering can result in the formation of new minerals and alteration of the rock's structure.
An example of physical weathering is when water freezes in cracks in a rock, causing it to expand and eventually crack. An example of chemical weathering is the reaction between water and limestone, which leads to the formation of caves and sinkholes.