The Rate and Extent of Chemical Change (Paper 2)

Question 1

How do catalysts speed up reactions?

Answer 1

by decreasing the activation energy needed for the reaction to occur

Question 2

What is the equation for the rate of reaction?

Answer 2

amount of reactant used or amount of product formed / time

Question 3

What are the units for rate?

Answer 3

g/s or cm cubed/s

Question 4

What are the 3 ways to measure the rate of a reaction?

Answer 4

• precipitation and colour change
• change in mass
• volume of gas

Question 5

How can you measure the rate of reaction through precipitation and colour change?

Answer 5

if the initial solution is transparent and the product is a precipitate which clouds the solution - how long it is until it changes (or vice versa)
or
observe a mark through the solution and measure how long it takes to disappear

Question 6

Define turbidity

Answer 6

if the cloudiness of a solution changes, its turbidity changes

Question 7

How can reversible reactions reach equilibrium?

Answer 7

as the reactants react, their concentrations fall so the forward reaction slows down. as more products are made and their concentrations rise, the backwards reaction speeds up
eventually the forward reaction will be going at the same rate as the backwards reaction - this is equilibrium

Question 8

What are the conditions that an equilibrium can be reached in?

Answer 8

a closed system - so none of the reactants or products can escape and nothing else gets in

Question 9

What does it mean if the equilibrium lies to the right?

Answer 9

more products have been made than reactants

Question 10

What does it mean if the equilibrium lies to the left?

Answer 10

more reactants are present than products

Question 11

What affects the position of the equilibrium?

Answer 11

1. the temperature
2. the pressure (gases only)
3. the concentrations of the reactants and products

Question 12

How does temperature affect the equilibrium?

Answer 12

it depends whether the forward and backward reactions are endothermic or exothermic

Question 13

What is an example of a reversible reaction being endothermic and exothermic?

Answer 13

thermal decomposition of hydrated copper sulfate:
if you heat blue hydrated copper crystals and evaporate the water -> endothermic
if you add water to anhydrous copper crystals -> exothermic

Question 14

What is Le Chatelier’s principle?

Answer 14

the idea that if you change the conditions of a reversible reaction at equilibrium, the system will try and counteract that change

Question 15

What can Le Chatelier’s principle be used for?

Answer 15

predicting the effect of any changes you make to a reaction system

Question 16

According to Le Chatelier’s principle, what happens when you change the pressure when a reaction is at equilibrium?

Answer 16

if the pressure is increased, the equilibrium reduces it by moving in the direction where there are fewer gas molecules and vice versa

Question 17

According to Le Chatelier’s principle, what happens when you change the temperature when a reaction is at equilibrium?

Answer 17

if the temperature is decreased, the equilibrium will move in the endothermic direction to produce more heat so more exothermic products are produced and vice versa

Question 18

According to Le Chatelier’s principle, what happens when you change the concentration when a reaction is at equilibrium?

Answer 18

if the concentration of the reactants is increased, the system responds by making more products to restore the equilibrium and vice versa