2.2 Rates Of Reaction

Question 1

What is collision theory

Answer 1

Reactant particles must collide with correct orientation and have sufficient kinetic energy for a reaction to occur

Question 2

Define activation energy

Answer 2

Minimum amount of energy required for a reaction to take place between 2 particles.

Question 3

How do you calculate rate

Answer 3

Amount of reactant used/product formed/ time (s)

Question 4

What are the factors affecting rate of reactions

Answer 4

concentration
pressure
Surface area of particle
temperature
catalysts
light

Question 5

How does temperature affect rates of reaction

Answer 5

There will be an increase in kinetic energy of the molecules and so they will move faster, so more molecules have enough energy to react on collision meaning the rate will increase so more effective collisions.

Question 6

How does particle size affect rate of reaction

Answer 6

Reducing particle size of a solid increases surface area so molecules are closer together and there is an increase in the number of collisions per unit time leading to an increase in reaction rate

Question 7

How does catalyst increase the rate of reaction

Answer 7

By providing a different pathway for the reaction that has a lower activation energy

Question 8

How does concentration (pressure) affect rates of reaction

Answer 8

If concentration of reactants increases, rate of reaction increases.
There are more molecules in the same volume so the distance between the molecules are reduced and there is an increase in the number of collions per unit time.
Therefore there is a greater chance that there will be a collision with energy greater than the activation energy so ROR INCREASES.

Question 9

How does pressure affect rate of reaction

Answer 9

More reacting particles in the same volume of gas so more frequent successful collisions

Question 10

Define catalyst

Answer 10

substance that speeds up the rate of a chemical reaction without being chemically changed at the end

Question 11

What is a homogenous catalyst

Answer 11

a catalyst that is in the same phase as all the reactants.
They take an active part in a reaction rather than being an inactive spectator.
Typically involves liquid mixtures or substances in solution
eg concentrated sulphuric acid in the formation of an ester

Question 12

What is a heterogenous catalyst

Answer 12

In a different phase from the reactants.
Many heterogenous catalysts are d block transition metals
Eg iron in the haber process for ammonia production

Question 13

How can you measure a rate of reaction when a gas is given off

Answer 13

Collect gas produced in an upside down measuring cylinder in a trough of water or in gas syringe to measure the volume of gas produced.
-measure the amount of gas collected over regular time intervals

Question 14

Define enzyme

Answer 14

globular proteins that act as homogenous catalysts in living systems

Question 15

What are enzymes used in

Answer 15

Rennin in the dairy industry
Yeast and amylase in the brewing industry
Lipase and protease in washing powders and detergent

Question 16

What are the benefits of using enzymes as catalysts

Answer 16

Lower temperatures and pressure used
Operate in mild conditions and dont harm fabrics or foods
Biodegradable
Allow reactions to take place which form pure products with no side reactions removing the need for complex separation techniques

Question 17

What are the benefits of using enzymes as catalysts

Answer 17

At higher temperature the peak moves to the right.
Higher energy with lower height.

Question 18

What are the benefits of using enzymes as catalysts

Answer 18

Increases the rate of a forward and backwards reaction by the same amount therefore doesn’t affect the position of equilibrium but it is reached more quickly.

Question 19

How does a catalyst affect an energy profile diagram

Answer 19

At the dame temperature a greater proportion of the reactant molecules will have sufficient energy to overcome activation energy for a catalysed reaction.

Question 20

How can you measure the rate of reaction using gas volume? How can you measure the rate of reaction using gas volume?

Answer 20

Record the volume of gas formed (e.g. Mg + HCl → MgCl₂ + H₂) using a gas syringe.

Question 21

How can gas pressure be used to study rate of reaction?

Answer 21

Measure pressure changes in reactions producing gases using a manometer (e.g. PCl₅ → PCl₃ + Cl₂).

Question 22

How is change in mass used to study rate?

Answer 22

Measure mass loss when gas escapes using a balance (e.g. CaCO₃ + HCl → CaCl₂ + CO₂).

Question 23

How is colorimetry used in studying rates?

Answer 23

Monitor colour change (e.g. iodine production) using a colorimeter to measure concentration change over time.

Question 24

What are the 3 specificed practicals for rates

Answer 24

GAS COLLECTIN
IODINE CLOCK
PRECIPITATION METHODS

Question 25

Describe a gas collection method

Answer 25

React a metal with acid (e.g. Mg + HCl). • Start the reaction by shaking the metal into the acid and start a stopwatch. • Measure the volume of hydrogen gas produced at regular intervals using a gas syringe or inverted burette. • Stop the timer when gas production stops. • Repeat with different acid concentrations, temperatures, or metal particle sizes, keeping all other variables constant. • Plot a graph of gas volume vs time to compare rates.

Question 26

Describe an iodine clock reaction

Answer 26

-Add measured volumes of acid, thiosulfate, iodine solution and starch to a conical flask. • Add a known volume of hydrogen peroxide to a test tube. • Rapidly pour peroxide into the flask and start a stopwatch. • Mix and stop the timer when the blue-black colour appears (iodine + starch). • Repeat with varying peroxide concentrations, keeping total volume constant. • Plot a graph of 1/time against [H₂O₂] to find the relationship between concentration and rate.

Question 27

Describe a precipitation reaction (Time taken for a precipitation or colour change)

Answer 27

Add thiosulfate solution to a conical flask and place it on a paper with a black cross. • Add nitric acid from a test tube to the flask, start a stopwatch, and mix. • Stop the timer when the black cross is no longer visible (due to sulfur precipitate). • Repeat with varying thiosulfate concentrations or acid concentrations, keeping total volume constant. • Plot 1/time against [S₂O₃²⁻] or [HNO₃] to find the effect on the rate of reaction.