C6

Question 1

How can you find the rate of a chemical reaction

Answer 1

Measure the quantity of reactant used or the quantity of product formed over time

Question 2

What formula is used to calculate rate of reaction

Answer 2

Mean rate = quantity of reactant used / time taken

       Or 

Mean rate = quantity of product formed / time taken

Question 3

What would be the correct units for rate if quantity were

A) mass measured in grams
B) volume measured in cm3
C) moles

Answer 3

A) g/s
B) cm3/s
C) mol/s

Question 4

If a reaction is to occur what 2 things need to happen between reacting particles

Answer 4

The particles must collide and they must collide with a minimum amount of energy (activation energy)

Question 5

Explain why increasing the temperature speeds up a reaction

Answer 5

It gives the particles more energy and they move faster so there are more frequent collisions and a higher proportion of collisions have at least the activation energy to react when they collide

Question 6

Explain why increasing the concentration of a solution speeds up a reaction

Answer 6

It means there are more particles in the same volume present so it will increase the frequency of collisions. More of these collisions will then have sufficient energy to react

Question 7

Explain why increasing the pressure on reactions involving gases speeds up the rate of reaction

Answer 7

Increasing the pressure increases the number of gas particles present in the same volume. This increases the frequency of collisions between reacting particles. More of these collisions will then have sufficient energy to react

Question 8

Explain how breaking up a solid reactant increases the rate of reaction

Answer 8

Breaking up a solid increases the surface area. This means that there is a greater area of solid and therefore the number of particles exposed for other particles to collide with. This increases the frequency of collisions. More of these collisions will have sufficient energy to react.

Question 9

What happens the the rate as a reaction progresses and what would a rate of reaction graph look like

Answer 9

Reactions start quickly and slow down as they progress. A rate curve will start off steep and the gradient will continually decrease to reflect the changing rate .

Question 10

What is a catalyst

Answer 10

A catalyst is a substance that speeds up the rate of a reaction without altering the products of a reaction, being itself unchanged chemically and in mass at the end of the reaction

Question 11

How does a catalyst speed up a reaction

Answer 11

a catalyst provides an alternative route which requires less activation energy

Question 12

What are enzymes and give one use of an enzyme in industry

Answer 12

Enzymes are biological catalysts and they can be used in the production of alcoholic drinks

Question 13

What is a reversible reaction

Answer 13

A chemical reactions in which the products of the reaction can react to make the original reactants

Question 14

What is meant by the term ‘dynamic equilibrium’

Answer 14

A reversible reaction is said to be in dynamic equilibrium when the rate of the forward reaction is equal to the rate of the backward reaction

Question 15

How can you change the equilibrium of a reversible reaction

Answer 15

By changing the conditions, for example temperature, pressure and concentration

Question 16

How does increasing the temperature affect the yield of C?
The production of C is exothermic

A + B = C
(= is reversible reaction sign)

Answer 16

Increasing the temperature always moves the equilibrium in the endothermic direction. In this process the backwards reaction is endothermic. Increasing the temperature reduces the yield of C.

Question 17

Explain how increasing the pressure effects the yield of Z

3X (g) + 2Y (g) = 2Z (g)

Answer 17

Increasing the pressure moves the equilibrium to the side of the equation with less molecules present.

Increasing the pressure increases the yield of Z

5 molecules of reactants are needed to make 2 molecules of Z. If the pressure is raised more Z is produced because that would reduce the number of molecules present.

Question 18

How would the position of dynamic equilibrium be affected by

A) temperature
B) pressure
C) concentration

Answer 18

A) increasing the temperature will move the dynamic equilibrium in the direction of the endothermic reaction
B) increasing the pressure will move the dynamic equilibrium towards the side where there are less gas molecules
C) increasing the concentration of a substance will move the equilibrium to reduce the concentration of that substance