Factors That Change Reaction Rate

Question 1

A reaction mixture is warmed from 20°C to 40°C while reactant amounts stay the same. What usually happens to the rate?

Accepted Answer

It increases because more collisions have enough energy to react.

Answer

It increases because the activation energy becomes lower.

Answer

It is unchanged because the concentrations stayed the same.

Answer

It decreases because dissolved particles move farther apart.

Question 2

Magnesium reacts with hydrochloric acid at 10°C and again at 30°C with the same acid concentration and magnesium surface area. Which trial is faster?

Accepted Answer

The 30°C trial, because particles collide with greater kinetic energy.

Answer

The 10°C trial, because cooler particles collide more gently.

Answer

Both trials, because temperature does not affect activation energy.

Answer

The 10°C trial, because the acid becomes more concentrated when cold.

Question 3

Why does storing milk in a refrigerator slow many spoilage reactions?

Accepted Answer

Lower temperature reduces the number of effective molecular collisions.

Answer

Lower temperature removes all catalysts from the milk.

Answer

Lower temperature increases the milk's surface area.

Answer

Lower temperature changes products back into reactants.

Question 4

In a sealed rigid container, a gas reaction is cooled from 300 K to 250 K while the gas amounts and volume stay fixed. How is the rate affected?

Accepted Answer

It decreases because the average collision energy is lower.

Answer

It increases because the activation energy disappears.

Answer

It stays the same because the container volume is unchanged.

Answer

It increases because every collision becomes effective.

Question 5

A sodium thiosulfate and acid reaction turns cloudy sooner at 32°C than at 22°C. Which explanation matches collision theory?

Accepted Answer

More particles have enough energy to form products at 32°C.

Answer

The reactant particles have less kinetic energy at 32°C.

Answer

The acid concentration must be lower at 32°C.

Answer

The reaction makes fewer collisions at 32°C.

Question 6

If an exothermic reaction mixture warms up as it runs, what can happen to its rate as the mixture gets hotter?

Accepted Answer

The rate can increase because particle speeds increase.

Answer

The rate must decrease because heat and temperature are the same thing.

Answer

The rate is forced to zero because products are warm.

Answer

The rate is unchanged because only catalysts affect rate.

Question 7

Two identical reactions are run at 25°C and 60°C. Which observation best fits the temperature effect on rate?

Accepted Answer

The 60°C reaction uses up a reactant sooner.

Answer

The 25°C reaction uses up a reactant sooner.

Answer

Both reactions must finish at exactly the same time.

Answer

The 60°C reaction stops because particles move too fast to collide.

Question 8

A reaction barely occurs at room temperature but goes quickly when heated. What changed most directly?

Accepted Answer

A larger fraction of collisions reached the activation energy.

Answer

Heating created new atoms that could react.

Answer

Heating changed the balanced equation coefficients.

Answer

Heating made every collision avoid the reactants.

Question 9

A solution reaction is repeated with double the concentration of one reactant. Why is the reaction usually faster?

Accepted Answer

Reactant particles collide more often per second.

Answer

Each particle has a lower molar mass.

Answer

The activation energy becomes infinite.

Answer

The products automatically become elements.

Question 10

Magnesium reacts more slowly after hydrochloric acid is diluted from 2.0 M to 0.50 M. What explains the slower rate?

Accepted Answer

There are fewer H+ ions per milliliter to collide with magnesium.

Answer

The H+ ions become heavier after dilution.

Answer

The magnesium surface area becomes larger after dilution.

Answer

The activation energy is lowered by adding water.

Question 11

A gas reaction is compressed to half its original volume at the same temperature. What rate change is expected?

Accepted Answer

The rate increases because gas particles collide more frequently.

Answer

The rate decreases because gas particles lose all kinetic energy.

Answer

The rate stays the same because gas pressure never affects rate.

Answer

The rate increases because gas particles become catalysts.

Question 12

Extra oxygen is added to a fixed-volume combustion chamber at the same temperature. How does this affect the reaction with fuel?

Accepted Answer

It increases the rate by increasing O2 concentration.

Answer

It decreases the rate by lowering the number of O2 collisions.

Answer

It keeps the rate unchanged because gases cannot change concentration.

Answer

It increases the rate by lowering every fuel molecule's mass.

Question 13

The pressure of a gaseous reactant is lowered while temperature stays constant. What happens to the reaction rate?

Accepted Answer

It decreases because fewer reactant particles occupy each liter.

Answer

It increases because particles spread out before colliding.

Answer

It stays the same because pressure and concentration are unrelated for gases.

Answer

It increases because the activation energy is used up.

Question 14

For H2(g) + I2(g) → 2HI(g), which change should increase the rate at the same temperature?

Accepted Answer

Increase the partial pressure of H2.

Answer

Increase the container volume without adding gas.

Answer

Remove some I2 from the container.

Answer

Lower the partial pressure of H2.

Question 15

A reaction uses 0.50 M acid, then is repeated with 1.50 M acid at the same temperature and surface area. What should happen?

Accepted Answer

It should be faster because acid particles are more crowded.

Answer

It should be slower because concentrated acid particles never collide.

Answer

It should be unchanged because molarity is not related to particles.

Answer

It should stop because higher concentration removes activation energy.

Question 16

Some dissolved reactant is removed before a reaction begins, making its concentration lower. What rate effect is most likely?

Accepted Answer

The rate slows because fewer reactant particles can collide.

Answer

The rate speeds up because particles have more empty space.

Answer

The rate is unchanged because only temperature affects collisions.

Answer

The rate speeds up because lower concentration is a catalyst.

Question 17

Calcium carbonate powder reacts faster with acid than one marble chip of the same mass. Which change explains the faster rate?

Accepted Answer

More CaCO3 surface is exposed to the acid.

Answer

The powder has a higher acid concentration.

Answer

The powder has less total CaCO3 mass.

Answer

Grinding lowers the activation energy like a catalyst.

Question 18

Iron wool rusts faster than an iron nail of the same mass. Why?

Accepted Answer

More iron atoms are exposed to oxygen and water.

Answer

Iron wool contains more total iron atoms than the nail.

Answer

Iron wool has a lower temperature than the nail.

Answer

Iron wool is consumed as a catalyst for rusting.

Question 19

Which aluminum sample should react fastest with acid if all samples have the same mass?

Accepted Answer

Aluminum foil cut into many tiny strips

Answer

One smooth aluminum cube

Answer

One tightly crumpled ball of foil

Answer

One thick aluminum bar with a polished surface

Question 20

An antacid tablet is crushed before it is dropped into water. What happens to the dissolving and reaction rate?

Accepted Answer

It increases because more tablet surface touches the liquid.

Answer

It decreases because smaller pieces have less contact with liquid.

Answer

It increases because crushing makes the water more concentrated.

Answer

It stays the same because surface area never affects solids.

Question 21

A magnesium ribbon is cut into filings without changing its mass. How should its reaction with acid change?

Accepted Answer

It should speed up because the exposed magnesium surface increases.

Answer

It should slow down because the magnesium atoms become smaller.

Answer

It should stop because cutting removes magnesium's reactivity.

Answer

It should stay the same because mass is the only solid factor.

Question 22

A 4 g zinc cube is replaced by four 1 g zinc pieces in the same acid. Why can the smaller pieces react faster?

Accepted Answer

Their total exposed surface area is larger.

Answer

Their total zinc mass is larger.

Answer

Their acid concentration is lower.

Answer

Their activation energy is higher.

Question 23

Which change would most likely decrease the rate of a solid sulfur reaction with oxygen?

Accepted Answer

Use larger sulfur chunks instead of sulfur powder.

Answer

Grind the sulfur chunks into powder.

Answer

Spread the sulfur in a thin layer.

Answer

Break the sulfur into smaller crystals.

Question 24

Why do many reactions involving a solid happen at the solid's exterior first?

Accepted Answer

Reactant particles collide with the solid at exposed surfaces.

Answer

Interior particles have zero kinetic energy in every solid.

Answer

Only the center of a solid contains atoms.

Answer

The exterior always has a higher concentration of catalyst.

Question 25

Manganese dioxide makes H2O2 decompose faster and is recovered unchanged. What role does it play?

Accepted Answer

It is a catalyst that provides a lower-activation-energy pathway.

Answer

It is a reactant that is used up to make oxygen.

Answer

It is a product that increases the final amount formed.

Answer

It is a solvent that lowers the concentration of H2O2.

Question 26

A catalyst is added to a reversible reaction at dynamic equilibrium. What is the direct rate effect?

Accepted Answer

It speeds the forward and reverse reactions by the same kind of lower-energy pathway.

Answer

It shifts equilibrium to products by speeding only the forward reaction.

Answer

It stops the reverse reaction by raising its activation energy.

Answer

It is consumed so the equilibrium expression changes.

Question 27

Compared with an uncatalyzed reaction path, what is true of a catalyzed path for the same reaction?

Accepted Answer

It has a lower activation energy.

Answer

It has different reactants and products.

Answer

It must have a larger ΔH.

Answer

It makes reactant particles collide less often.

Question 28

Only a small amount of enzyme is needed to speed a reaction in a lab demo. Why can it keep working?

Accepted Answer

The enzyme is regenerated after each catalytic cycle.

Answer

The enzyme is permanently converted into product.

Answer

The enzyme raises the activation energy each time.

Answer

The enzyme supplies all atoms in the products.

Question 29

A reaction runs quickly while a catalyst is present, then slows when the catalyst is removed. What changed?

Accepted Answer

The lower-activation-energy pathway was no longer available.

Answer

The balanced equation changed to remove products.

Answer

The reactant concentration instantly doubled.

Answer

The reaction became impossible at any temperature.

Question 30

A catalyst and a temperature increase can both speed up a reaction. How is the catalyst's effect different from heating?

Accepted Answer

It lowers the activation energy instead of giving particles more kinetic energy.

Answer

It gives particles more kinetic energy instead of lowering the activation energy.

Answer

It raises reactant concentration instead of changing collision energy.

Answer

It increases the amount of product formed instead of the rate.

Question 31

Platinum in a catalytic converter speeds reactions of exhaust gases. What is platinum doing?

Accepted Answer

Providing a surface pathway that lowers activation energy

Answer

Being completely consumed as the main fuel

Answer

Increasing the final number of atoms formed

Answer

Diluting the exhaust gases so they collide less often

Question 32

Two identical mixtures form the same maximum amount of product, but the catalyzed one gets there sooner. What did the catalyst change?

Accepted Answer

The rate, not the amount of product possible from fixed reactants

Answer

The number of atoms conserved in the reaction

Answer

The identity of every product molecule formed

Answer

The stoichiometric coefficients of the balanced equation

Question 33

Trial 1: 20°C, 1.0 M acid, metal strip. Trial 2: 40°C, 1.0 M acid, metal strip. Trial 3: 20°C, 2.0 M acid, strip. Which trial tests temperature against Trial 1?

Accepted Answer

Trial 2

Answer

Trial 3

Answer

Trials 2 and 3 together

Answer

Neither trial

Question 34

A: 20°C, 0.5 M acid, powder. B: 20°C, 1.0 M acid, powder. C: 40°C, 0.5 M acid, powder. D: 20°C, 0.5 M acid, chunk. Which pair isolates concentration?

Accepted Answer

A and B

Answer

A and C

Answer

A and D

Answer

B and D

Question 35

Four 2 g calcium carbonate samples react with acid at 25°C: large chip 90 s, small chips 55 s, powder 22 s, large chip in more dilute acid 140 s. Which sample reacted fastest because of its greater surface area?

Accepted Answer

Powder, 22 s

Answer

Large chip, 90 s

Answer

Small chips, 55 s

Answer

Large chip with dilute acid, 140 s

Question 36

Trial A uses no catalyst and produces 30 mL gas in 120 s. Trial B is identical but uses a catalyst and produces 30 mL gas in 45 s. What is Trial B's average rate of gas production?

Accepted Answer

0.67 mL/s

Answer

0.25 mL/s

Answer

1.5 mL/s

Answer

0.38 mL/s

Question 37

Gas trials at 300 K use the same reactants. Trial 1: 1.0 L container, slow. Trial 2: 0.50 L container, faster. Which factor most likely caused the faster rate?

Accepted Answer

Higher gas pressure and concentration in the smaller volume

Answer

Lower gas pressure in the smaller volume

Answer

Lower collision frequency in the smaller volume

Answer

A larger solid surface area in Trial 2

Question 38

CaCO3 trials: 1) 20°C, 1.0 M, chip. 2) 20°C, 1.0 M, powder. 3) 40°C, 1.0 M, chip. 4) 20°C, 2.0 M, chip. Which comparison tests surface area?

Accepted Answer

Trial 1 and Trial 2

Answer

Trial 1 and Trial 3

Answer

Trial 1 and Trial 4

Answer

Trial 3 and Trial 4

Question 39

Without a catalyst, a reaction has an activation energy of 75 kJ/mol and ΔH = -40 kJ/mol. Which values could describe the same reaction with a catalyst?

Accepted Answer

Activation energy 50 kJ/mol, ΔH = -40 kJ/mol

Answer

Activation energy 50 kJ/mol, ΔH = -20 kJ/mol

Answer

Activation energy 95 kJ/mol, ΔH = -40 kJ/mol

Answer

Activation energy 75 kJ/mol, ΔH = -65 kJ/mol

Question 40

A reaction reaches cloudiness in 80 s at 15°C, 40 s at 25°C, and 20 s at 35°C. Which factor matches this trend?

Accepted Answer

Higher temperature makes the reaction faster.

Answer

Lower concentration makes the reaction faster.

Answer

Lower surface area makes the reaction faster.

Answer

Removing a catalyst makes the reaction faster.

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Factors That Change Reaction Rate

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Factors That Change Reaction Rate

Ways to Play

Device Games: Students play on their phones

Blast Go

Zombie Escape

Avalanche

Maze Blast

Cave Climb

Blast Out

Mystery Auction

Tour Guide

Food Truck Rush

Tug of War

Alien Blast

Glacier Rush

Board Games: Teacher-led, projected to the class

Like what you see?

More like this

Bug Blast

BlastRace

BlastQuiz

BlastBoard

Seek & Destroy

Mystery Blast

Checkers

Texas Hold 'Em

Da Bomb

Castle Siege

Hot Potato

Market Mayhem

King of the Hill

Bank Heist

Top Corner