Rate and equilibria

Question 1

What do we look at to measure the rate of a chemical reaction?

Answer 1

How quickly the reactants are used up or how quickly the products of the reaction are made

Question 2

What are the three ways to take the measurements of the rate of a chemical reaction?

Answer 2

Measuring the mass of a reaction mixture
Measuring the volume of gas given off
Measuring the time for a visual change like precipitation

Question 3

How do we calculate the mean rate of a reaction?

Answer 3

Mean rate of reaction = amount of reactant used or amount of product formed / time

Question 4

What are the four factors that affect the rate of a chemical reaction?

Answer 4

Temperature
Surface area
Concentration of solutions / pressure of gases
A catalyst

Question 5

Why do more collisions of particles result in a faster reaction?

Answer 5

Because a higher proportion of particles have energy greater than the activation energy

Question 6

What is the affect of surface area on the rate of a reaction?

Answer 6

If the surface area of any solid reactant is increased (e.g. crushed up / cut into smaller pieces) then the rate of reaction will increase as this increases the frequency of collisions

Question 7

What is the affect of temperature on the rate of a reaction?

Answer 7

When we increase the temperature of a reaction it always increases the rate of the reaction because the particles gain more energy, causing more frequent collisions

Question 8

What are the affects of concentration and pressure on the rate of a reaction?

Answer 8

Increasing the concentration or pressure of reactants increases the number of particles per cm³ which causes the frequency of collisions to increase (increasing the pressure meaning reducing the size of the container of gas)

Question 9

How does a catalyst work?

Answer 9

It works by providing an alternative route with a lower activation energy, causing more particles to have energy greater than the activation energy and increasing the number of collisions

Question 10

What are two examples of catalysts?

Answer 10

Iron in the Haber process to make ammonia
Platinum used in the production of nitric acid

Question 11

Do catalysts have an affect on the position of equilibrium?

Answer 11

They have no effect on the position of equilibrium so they do not alter the composition of the equilibrium mixture

Question 12

What happens to a reversible reaction in a closed system?

Answer 12

No reactants, products or energy can get in or out
and equilibrium is reached when the rates of both the forwards and backwards reactions become equal

Question 13

What happens to the position of equilibrium if temperature is raised?

Answer 13

The position of equilibrium moves in the endothermic direction to cool down the system

Question 14

What happens to the position of equilibrium if temperature is lowered?

Answer 14

The position of equilibrium moves in the exothermic direction to heat up the system

Question 15

What happens if the concentration of a reactant is increased?

Answer 15

More products will be formed to decrease the concentration of the reactants

Question 16

What happens if the product concentration is decreased?

Answer 16

More reactants will react to increase the concentration of the products

Question 17

What happens to the position of equilibrium if pressure is raised?

Answer 17

The position of equilibrium moves to the side with the fewest gas molecules to reduce the pressure

Question 18

What happens to the position of equilibrium if pressure is lowered?

Answer 18

The position of equilibrium moves to the side with most gas particles to increase the pressure

Question 19

What is the process of
manufacturing ammonia?

Answer 19

1) Nitrogen from the air and hydrogen from methane are used
2) The purified gases are compressed (at 200 atmospheres) and heated (at 450 degrees celsius)
3) The mixture is passed over a hot catalyst of iron and some of the nitrogen and hydrogen combine to give ammonia
4)The unreacted nitrogen and hydrogen continue to be passed over the catalyst
5) The mixture is cooled and has now formed liquid ammonia

Question 20

Why can’t we use a higher pressure to form even more ammonia?

Answer 20

Because it would require lots of energy and be expensive

Question 21

Why can’t we use a lower temperature to form even more ammonia?

Answer 21

Although lower temperatures would increase the amount of ammonia produced, it would be produced too slowly

Question 22

What affect does a catalyst have on the production of ammonia?

Answer 22

A catalyst does not affect the actual yield of ammonia but we do get it formed quicker