4.6.1.2 RATES OF CHEMICAL REACTIONS

Question 1

what factors affect the rates of chemical reactions and how?

Answer 1

factors: the concentrations of reactants in solution, the pressure of reacting gases, the surface area of solid reactants, the temperature and the presence of catalysts.
how: increasing these factors will increase the rate of reaction, as it will take less time for the reaction to take place. It is the same when a catalyst is present.

Question 2

what happens if concentration and pressure increase?

Answer 2

• there are more reactant particles per unit volume (i.e. the reactant particles become more crowded)
• there is a greater chance of the particles colliding, which leads to more successful collisions per second
• the rate of reaction increases

Question 3

what happens if temperature increases?

Answer 3

• the reactant particles move more quickly
• they have more energy
• the particles collide successfully more often
• the rate of reaction increases
• this is due to more particles having energy greater than or equal to the activation energy

Question 4

how do you increase surface area?

Answer 4

cutting the substance into small pieces, or by grinding it into a powder

Question 5

do larger pieces or smaller pieces/powder have a large surface area?

Answer 5

smaller pieces/powder have a larger surface area

Question 6

what happens when the surface area of the reactant increases?

Answer 6

• more particles are exposed to the other reactant
• there is a greater chance of particles colliding, which leads to more successful collisions per second
• the rate of reaction increases

Question 7

what is a catalyst?

Answer 7

A catalyst is a substance which changes the rate of reaction but is unchanged at the end of the reaction

Question 8

why is a catalyst specific to a particular reaction?

Answer 8

• different catalysts catalyse different reactions
• not all reactions have suitable catalysts

Question 9

how much of a catalyst is needed to increase the rate of reaction between large amounts of reactants?

Answer 9

Only a very small amount of catalyst is needed

Question 10

what does an iron catalyst catalyse in a reaction?

Answer 10

Making ammonia from nitrogen and hydrogen

Question 11

what does a platinum catalyst catalyse in a reaction?

Answer 11

Making nitric acid from ammonia

Question 12

what does a Vanadium(V) oxide catalyst catalyse in a reaction?

Answer 12

Making sulfuric acid