Chemistry Topic 6- RoR

Question 1

Why are rates of reaction important in industry?

Answer 1

The faster you make chemicals, the faster you make money

Question 2

Give 2 examples of a slow reaction

Answer 2

1. The rusting of iron

2. Chemical weathering- like acid rain damage to limestone buildings

Question 3

Give an example of a moderate speed reaction

Answer 3

Magnesium reacting with an acid to produce a gentle stream of bubbles

Question 4

Give 2 examples of a fast reaction

Answer 4

1. Burning

2. Explosions- they are faster and release a lot of gas. They are over in a fraction of a second

Question 5

How can you find the speed of a reaction?

Answer 5

By recording the amount of product formed (or amount of reactant used up) over time

Question 6

What does a flat line on a RoR graph show?

Answer 6

The reaction has finished

Question 7

1. What does the rate of a chemical reaction depend on?

2. What is this theory called?

Answer 7

1. The collision FREQUENCY of the reacting particles AND the ENERGY TRANSFERRED during the collision (particles need to collide with enough energy to be successful)
2. Collision theory

Question 8

What is ACTIVATION ENERGY?

Answer 8

The minimum amount of energy needed for the particles to react. This is the energy needed to break the bonds in the reactants.

Question 9

What are the 4 things that increase the RoR?

Answer 9

1. Temperature
2. Concentration/ Pressure
3. SA
4. Catalyst

Question 10

How does temperature increase RoR?

Answer 10

1. Increased temp means particles move faster so they collide more and will have more energy so more successful collisions

Question 11

How does increasing concentration/ pressure increase RoR?

Answer 11

There are more particles in the same amount of space so more frequent collisions

Question 12

How does increasing SA increase RoR?

Answer 12

More frequent collisions as there is more area to work on

Question 13

How can you increase SA?

Answer 13

By breaking something into smaller pieces- will increase its SA:V

Question 14

What is a catalyst?

Answer 14

A substance that speed up a reaction, but isn’t used up in the reaction itself (so it’s not part of the overall reaction equation)

Question 15

How does using a catalyst increase the RoR?

Answer 15

It decreases the activation energy by providing an alternative reaction pathway

Question 16

What is the equation for RoR?

Answer 16

Rate of reaction= amount of reactant used or amount of product used / time

RoR in cm3/s (for a gas) or g/s (for a solid) or mol/s

Question 17

What are 3 ways of MEASURING the RoR?

Answer 17

1. Precipitation and Colour Change
2. Change in Mass (Usually Gas Given Off)
3. Volume of has given off

Question 18

How does precipitation and colour change work? + disadvantages

Answer 18

1. You can observe the visual change using a mark under the initial transparent solution and waiting for it to precipitate which will block out the mark
2. The results are subjective
   Can’t plot a RoR graph

Question 19

How does change in mass work? + ads and disads

Answer 19

If the reaction produces a gas, you can measure the mass of the reaction at regular intervals throughout the reaction

Ads- can plot a RoR graph
Most accurate of the 3 methods

Disads- releasing the gas straight into the room

Question 20

How does the volume of gas given off work? + ads and disads

Answer 20

You collect gas given off in a gas syringe, the more given off during a given time interval, the faster the reaction

Ads- fairly accurate
Can plot a RoR graph

Disads- Have to be careful because of the reaction is too vigorous, you can blow the plunger out of the end of the syringe

Question 21

Mg ribbon + dilute hydrochloric acid (HCl) —> …?

What method can you use to measure RoR?

What else could we investigate and how could we keep it a fair test?

Answer 21

1. Hydrogen gas
2. Volume of gas given off. You can plot a graph with time on X axis and volume of gas produced on Y axis
3. The effect of using different acid concentrations- make sure to use the same volume of acid and amount of Mg ribbon

Question 22

1. Sodium Thiosulfate and HCl —> what sort of precipitate?
2. What method could you use?
3. Disadvantage?

Answer 22

1. A cloudy, yellow precipitate of sulfur
2. Precipitation/ colour change method
3. The reaction releases sulfur dioxide, so the experiment should be carried out in a well-ventilated place

Question 23

• Sodium thiosulfate and HCl produce a cloudy precipitate
• You can investigate how the concentration of acid affects the rate

How can you make it a fair test?

How can you draw a graph of an approximate RoR?

Answer 23

1. Only change the concentration of 1 reactant at a time
   Keep the depth of the liquid the same
2. You can’t normally draw a graph because all you get is a set of reading of how long it took till the mark disappeared
   However you could draw a graph of concentration against 1/time which will give you an approximate rate

Question 24

How can you calculate the mean RoR from a graph

Answer 24

Change in Y / change in X

Question 25

How do you calculate the RoR at a particular point in time?

Answer 25

Draw a tangent to the curve at that point

Then calculate the gradient using change in Y/ change in X