Rates Of Reactions

Question 1

At the the start of a reaction what would the amount of reactants be? And at the the end of a reaction what would the amount of reactants be?

Answer 1

Start-high

End-low

Question 2

What happens to the amount of reactants as a reaction takes place? And when does the amount of reactants change fastest?

Answer 2

It decreases

At the start

Question 3

How could you sketch a graph to show what happens to the amount of reactants during a reaction?

Answer 3

Draw a graph of concentration(mol/dm³)[y] against time(s)[x]
The graph would be a curve starting high on the concentration curving down towards time and levelling out (like the shape of an elongated l)

Question 4

How could you sketch a graph to show what happens to the amount of products during a reaction?

Answer 4

Draw a graph of concentration(mol/dm³)[y] against time(s)[x]

The graph would be a curve starting at the origin curving up and levelling out(like the shape of an f without the cross)

Question 5

How can it be shown on a graph that a reaction has finished?

Answer 5

When the gradient = 0

Question 6

How should you draw a graph with a line of best fit?

Answer 6

You should draw either a straight line or curve which goes through the greatest amount of point whilst ignoring anomalies, you should circle any anomalies you find

Question 7

What do you observe when calcium carbonate reacts with an acid?

Answer 7

It fizzes, gas is produced

Question 8

What’s an experiment which investigates the effect of surface area on the rate of reaction?

Answer 8

Calcium carbonate(marble) and hydrochloric acid

• use 2g of large marble chips and 2g of small marble chips
• put the large marble chips, a conical flask with HCl in and cotton wool on a set of weighing scales and set the mass to 0
• add the marble chips to the conical flask and put the cotton wool on
• start the stopwatch and record the mass at 30second intervals until the mass is consistent
• repeat with the small marble chips

Question 9

What does a curve on a graph of a reaction show?

Answer 9

That the rate of reaction is changing

Question 10

In terms of collisions of particles explain the relationship between surface area and the rate of reaction?

Answer 10

As the particle size of a set mass decreases the surface area increases so there’s a higher rate of collisions per second therefore there’s an increased rate of reaction

Question 11

In the reaction between calcium carbonate and acid why is it important to put cotton wool in the neck of the conical flask?

Answer 11

It prevents acid from splashing and escaping effecting the mass reading but allows carbon dioxide to escape

Question 12

What’s an experiment which investigates the effect of reactant concentration on the rate of reaction?

Answer 12

• use different concentrations of HCl and use 2g of marble chips
• put the acid in a conical flask with a bung and gas syringe attached
• add the marble chips and time how long it takes for 20cm³
• then repeat with different concentrations of acid

Question 13

What’s rate of reaction proportional to?

Answer 13

1/t

Question 14

In terms of particles and collisions what is the effect of concentration on rate of reaction? And what would a graph showing this look like?

Answer 14

-more particles in a given volume
-particles will be closer together
-higher collision frequency
-higher rate of reaction
Graph-would be a straight line starting from the origin(directly proportional)

Question 15

In reactions between gases what can be done to bring the particles closer together?

Answer 15

Increasing the pressure

Question 16

What’s the relationship between pressure and rate of reaction?

Answer 16

The higher the pressure the quicker the rate of reaction

Question 17

What’s the disadvantage of gas collection for measuring rate of reaction?

Answer 17

• loss of initially produced gas

- high concentration experiments lead to measurement of a short period of time

Question 18

What’s the disadvantage of mass loss for measuring rate of reaction?

Answer 18

-balance can not be precise

Question 19

What’s an experiment to investigate the effect of temperature on rate of reaction?

Answer 19

• use the same concentration and volume of sodium thiosulfate and hydrochloride acid
• put the sodium thiosulfate in different temperature water baths then add the acid to a conical flask over a x on a piece of paper
• add the sodium thiosulphate with a thermometer and then start the stop watch
• time how long it takes for you to no longer be able to see the x and repeat this experiment with different temperatures

Question 20

Why should a graph of temperature against rate not start at the origin?

Answer 20

Because at 0°C the reaction can still take place

Question 21

When do reactions occur when particles collide?

Answer 21

When they have the needed activation energy

• activation energy is the minimum energy required for a reaction to take place
• most collisions don’t have the required activation energy
• if the activation energy is high then the rate of reaction is low because there are less successful collisions

Question 22

In terms of particles how does temperature affect the rate of reaction? And what would a graph of temperature and rate of reaction look like?

Answer 22

-higher temp, particles move faster(have more kinetic energy)
-collide more frequently
-greater proportion of successful collisions
-rate of reaction increases
Graph-curve not directly proportional

Question 23

What does a catalyst do in a reaction?

Answer 23

It increases the rate of reaction by providing a more obtainable activation energy and it isn’t used up in the reaction
It provides a different route with a lower activation energy so more particles collide with the activation energy

Question 24

Define a catalyst:

Answer 24

Speeds up reactions and they aren’t used up in the reaction

Question 25

How would you sketch an energy profile of a reaction with and without a catalyst?

Answer 25

You draw the axis
They draw a level straight line and label it reactants
Then carry on this line but draw a really stretched high n without the stick and label the peak the activation energy
They carry on the n lower than the straight line for reactants then stop and draw a lower level straight line and label it products
*for the energy profile of a reaction with a catalyst you draw the n with a lower peak