C6 The Rate and Extent of Chemical Change random revision pages 142 - 148

Question 1

What is rate of reaction a measure of?

Answer 1

How quickly reactants are changed into products

Question 2

How can you tell what line on a rate graph respresnts the fastest rate of reaction? how can you tell?

Answer 2

It is the line that starts more steeply and goes flatter sooner than any of the others

Question 3

What does collision theorty state must happen in order for a reaction to take place?

Answer 3

Particles must colide with enough energy to react (this is the activation energy).

Question 4

What could you do in order to increase the speed at which particles in a reaction are moving?

Answer 4

increase the temperature

Question 5

Explain why breaking up a solid into smaller pieces will increase its rate of reaction?

Answer 5

Breaking a solid into smaller pieces increases its surface area/surface area to volume ratio. More of the solid’s particles are available to particles of the other reactant and so collisions will be more frequent.

Question 6

Catalysts provide an alternative reaction pathway. How does this pathway affect the rate of reaction? Explain your answer.

Answer 6

It increases the rate of reaction. The alternative pathway has a lower activation energy, so less energy is needed for the reaction to take place.

Question 7

Which units are usually used to measure the volume of gas produced by a reaction?

Answer 7

cm³

Question 8

What is meant by the ‘turbidty’ of a solution?

Answer 8

its cloudiness.

Question 9

State one disadvantage of using a change in colour/turbidity to measure the rate of a reaction?

Answer 9

Any one from:

The results are very subjective.

You can’t plot a rate of reaction graph from the results.

Question 10

A reaction produces a gas. State one thing you could measure to determine the rate of this reaction, and the piece of equipment you would use to measure it?

Answer 10

Any one from:

Measure the change in mass using a mass balance.

Measure the volume of gas given off using a gas syringe.

Question 11

A student carries out an experiment to determine the effect of concentration on reaction rate. Why is it important that the student conrols all other variables in this experiment?

Answer 11

To make it a fair test./ So the student knows that any differences in reaction rate are due to differences in concentration and not a result of something else.

Question 12

Give two things that should be kept constant when investigating the effect of acid concentration on the rate of the reaction between dilute acid and marble chips?

Answer 12

Any two from:

Mass of marble chips.

Surface area of marble chips.

Volume of acid.

Temperature

Question 13

A student measures the rate of reaction between hydrochloric acid and magnesium using a mass balance. Why should the student plug the reaction vessel with cotton wool in this experiment?

Answer 13

To stop the acid spitting out (while still letting the gas escape).

Question 14

Sodium thiosulfate and hydrochloric acid react to product a cloudy precipitate. Describe a method you could use to investigate the rate of this reaction?

Answer 14

E.g.

Add a set volume of dilute sodium thiosulfate solution to a conical flask.

Place the flask on a piece of paper with a black cross drawn on it.

Add a set volume of dilute hydrochloric aicd to the flask and start a stopwatch.

Measure the time taken for the cross to disappear from view.

Question 15

Which variable should go on the x-axis of a rate graph? What about the y-axis?

Answer 15

x-axis = time
y-axid = amount of reactant used or amount of product formed.

Question 16

What does a flat line on a rate of reaction graph tell you?

Answer 16

The reaction has finished.

Question 17

What does this symbol tell you about a reaction?

> > > > > > > > > > > > > > «««««««<

Answer 17

The reaction is reversible.

Question 18

True of false? Equilibrium can only be reached if the reaction takes place in a closed system. Explain your answer

Answer 18

True, because in order for equilibrium to be reached, none of the reactants or products can escape and nothing else can get in.

Question 19

In the reaction shown below, more ammonium chloride breaks down and more the reaction mixture is heated. How could you change the conditions to increase the amount of ammonium chloride present?

ammonium chloride &raquo_space;»
«&laquo_space; ammonia +
hydrogen chloride

Answer 19

Decrease the temperature.

Question 20

If a reversible reaction gives out a certain amount of heat in one direction, what can you say about the energy change in the other direction?

Answer 20

The same amount of energy will be taken in./It will be endothermic

Question 21

What principle is used to predict the effects of changing the conditions of a reaction at equilibrium?

Answer 21

Le Chatelier’s Principle

Question 22

What will happen to the position of equilibrium in a reversible reaction if the temperature is increased, and the forward reaction is exothermic?

Answer 22

The equilibrium will move to the left/to favour the endothermic direction.

Question 23

Explain how increasing the pressure would effect an equilibrium involving gasses?

Answer 23

The equilibrium position would shift towards the side of the reaction equation with fewer molecules of gas in order to reduce the pressure.