Rates of Reaction

Question 1

Mean rate of reaction = ?

Answer 1

quantity of reactant used / time taken

quantity of product formed / time taken

Question 2

Units for rate of reaction?

Answer 2

g/s or cm3/s

Question 3

How to calculate the mean rate of reaction and a specific time?

Answer 3

Draw a tangent to the curve at the time
Construct a right angled triangle, using the tangent as it’s hypotenuse
Rate of reaction = change in y/ change in x

Question 4

The steeper the line on the graph?

The gradient tells us?

Answer 4

the greater the rate of reaction

the rate of reaction

Question 5

What happens over time to the graph line?

Answer 5

It starts of the steepest. However, over time, it becomes less and less steep as reactants are used up and eventually flat when the reaction stops

Question 6

The quickest reactions have?

Answer 6

the steepest lines and becomes flat in the least time

Question 7

Name 3 methods for measuring either

1. How fast the reactants are used up
2. How fast the products of the reaction are made

Answer 7

1. Measuring decreasing mass of a reaction mixture
2. Measuring the increasing volume of gas given off
3. Measuring decreasing light passing through a solution

Question 8

x axis:

y axis:

Answer 8

x axis: time (s)

y axis: factor being measured: volume/mass - cm3 / g

Question 9

What are 5 factors that can vary the rate of reaction?

Answer 9

1. The temperature
2. The pressure (for reactions with gaseous reactants)
3. The concentration of solutions (when relevant)
4. The surface area of solid reactants
5. The presence of catalysts

Question 10

Using collision theory, explain the effect of increasing temperatures on rate

Answer 10

Increasing temperature means increasing the amount of energy the particles have. This means the particles move faster, meaning more frequent collisions and therefore more frequent successful collisions, equalling an increased rate of reaction
As well as this, more energy means the likelihood of particles colliding with the activation energy increases, meaning more frequent successful collisions, equalling an increased rate of reaction

Question 11

Using collision theory, explain the effect of increasing concentration/pressure on rate

Answer 11

If a solution is more concentrated, it means there are more particles in the same volume of solvent
Similarly, when the pressure of a gas increases, it means the same number of particles occupy a smaller space
This means more frequent collisions, and therefore more frequent successful collisions, increasing the rate of reaction.

Question 12

Using collision theory, explain the effect of increasing surface area on rate

Answer 12

For a given mass of solid, large lumps have smaller surface area to volume ratio than smaller lumps or powders.
If a large lump is divided or ground to a powder
1. It’s total volume stays the same
2. Are of exposed surface increases
3. Surface area to volume increases
This means more frequent collisions and therefore more frequent successful collisions, increasing the rate

Question 13

What is a catalyst?

Answer 13

Catalysts increase the rate of chemical reactions but are not used up during the reaction. Different reactions need different catalysts.

Question 14

Explain how catalysts work

Answer 14

Catalysts increase the rate of reaction by providing a different pathway for the reaction that has a lower activation energy, meaning more frequent successful collisions, increasing the rate of reaction.

Question 15

Sketch a reaction profile for a catalysed reaction

Answer 15

https://www.chemguide.co.uk/physical/basicrates/energyprofiles.html

Question 16

Investigations into rate of reaction?

Answer 16

measure the volume of gas produced when marble chips react with different concentrations of hydrochloric acid
measure how long it takes for no change in mass to occur (no more gas produced) when reacting hydrochloric acids with large, small and powdered marble chips