Chapter 10 - Rates of reaction

Question 1

What is the equation for the rate of a reaction ?

Answer 1

Rate = 1
——
time

Question 2

What are the units for rate ?

Answer 2

s^-1

Question 3

How do you experimentally investigate reactions that produce a gas ?

Answer 3

the volume of gas produced or the mass of the gas lost can be measured

Question 4

How do you measure the amount of gas produced per unit time ?

Answer 4

• a stopwatch is started and the gas is collected in a gas syringe
• the reaction is over when two of the gas readings are the same
• no more gas is being produced because one of the reactants has been used up

Question 5

How do you measure the change in mass in a given time ?

Answer 5

• Place a conical flask with the reaction mixture in it onto a top-pan balance
• place a cotton wool plug at the top of the conical flask
• start a stopwatch and record the mass at regular intervals

Question 6

Why is the cotton wool plug used ?

Answer 6

to let the gas out but to stop any liquid escaping the conical flask

Question 7

How do you measure the rate of a precipitation reaction ?

Answer 7

• place the reaction flask containing one reactant solution on top of a piece of paper with an x on it
• record the time taken after the second solution is added for the x to not be visible through the solution

Question 8

What is the definition of activation energy ?

Answer 8

Activation energy is the minimum energy needed for a reaction to occur

Question 9

How does temperature affect the rate of a reaction ?

Answer 9

• particles have increased kinetic energy, so move faster
• more frequent collisions
• more activation energy so more successful collisions
• so rate of the reaction is faster

Question 10

How does concentration affect the rate of a reaction ?

Answer 10

• more particles present in the same volume
• more successful collisions between particles in a given time
• and so rate of reaction is faster

Question 11

How does surface are affect the rate of a reaction ?

Answer 11

• there are more particles on the surface exposed to the reactant
• so more successful collisions occur in a given time
• and so the rate of the reaction is faster

Question 12

What is a catalyst ?

Answer 12

A catalyst is a substance that increases the rate of a reaction without being used up

Question 13

How does a catalyst work ?

Answer 13

A catalyst works by :

• providing an alternative reaction pathway of lower activation energy
• and so more successful collisions between particles in a given time
• and so the rate of the reaction is faster