Rate Of Reaction

Question 1

Define rate of reaction?

Answer 1

The rate of chemical reaction tells you how fast reactants turn into products

Equation = Amount of energy used or amount of product formed / time

Question 2

What is activation energy?

Answer 2

The minimum energy needed for the start of a reaction

Question 3

What is collision theory?

What are the ways to increase rate of reaction?

Answer 3

Particles colliding with sufficient energy (activation energy) for a reaction to take place. Increasing the number of collisions or increasing the energy for each particle will increase the rate of reaction

To increase the chance of particles reacting to increase rate of reaction:

1. Increasing temperature makes particles move faster, colliding more frequently and more collisions have activation energy
2. Increasing concentration - more particles in the same area mean more frequent collisions
3. Increasing surface area - particles are exposed so collide more often

Question 4

What is concentration?

Answer 4

The amount of substance (solute) dissolved in a certain volume of a solution

Question 5

What is a catalyst?

What types of catalysts are used in biological processes?

Answer 5

A substance that speeds up a chemical reaction without being used up itself and without changing chemically.

Catalyst lowers the activation energy level so more reactant particles have the energy to react.

Biological processes use enzymes - large protein molecules accommodating substrates - as catalysts

In industries catalysts make reactions quicker, cheaper and with less waste but it must be safe. It means less fossil fuels so less carbon dioxide in the air.

Catalysts can be used again and again but eventually become poisoned by the reaction mixture and stop working (become denatured).

Question 6

Give an example of a catalyst?

Answer 6

Manganese oxide will speed up the reaction that makes hydrogen peroxide decomposing into water and oxygen
H2O2 -> O2 + H2O

The presence of oxygen is shown by relighting a glowing splint

Question 7

What is a reversible reaction?

Answer 7

A reaction in which the products can reform as the reactants

Question 8

What is a tangent?

Answer 8

The tangent to the curve on a graph. The gradient Is the instantaneous rate of reaction. It is a straight line that touches the point on the curve of a line on a graph

Question 9

What is gradient?

Answer 9

Steepness of a line on a graph - the steeper the graph the faster the rate of reaction
When one or all reactants are used up the gradient flattens

Chemical gradient is difference in solute concentration across a membrane
Electrical gradient is difference in charge across a membrane

Question 10

Rates of reaction in order?
Rusting
Rain dissolving limestone buildings
Burning coal
Dynamite explosion

Answer 10

1. Dynamite explosion
2. Burning coal
3. Rusting
4. Rain dissolving limestone buildings

Question 11

What do we measure the amount of reactants or products in?

How do we show the rate of reaction?

Answer 11

Measure by mass, volume or colour
Display by graph - steeper line equals faster rate of reaction
Calculate the slope gradient to give rate
Gradient = rate of reaction

Question 12

How do you investigate the rate of reaction between marble chips and acid?

Answer 12

The size of chips is the independent variable that changes
The volume of gas is the dependent variable that you measure
The volume of acid and mass of chips (at the beginning of the experiment) is the control variable

Sodium thiosulpate + hydrochloric acid makes yellow sulphur solid that eventually builds up and obscures underneath the flask

Question 13

Explain the two types of reaction calculations?

Answer 13

The mean rate of reaction shows the average and is based on the total amount of product made/the total time taken
The specific rate of reaction at any point is found by using the tangent - change in y/change in x

Question 14

How do you measure decreasing mass of a reaction mixture?

Answer 14

Use a top-pan balance and carry out the reaction in a conical flask and a cotton bung.
The bung prevents gas escaping and keeps measurements accurate.
Record and measure the mass at regular time intervals.

Question 15

How do you measure the increasing volume of gas given off?

Answer 15

Collect the gas and measure its volume at intervals to find rate of reaction.
Use gas syringe to collect and measure gas given off.
Make sure conical flask is air tight so no gas escapes using a bung.

Question 16

How do you measure decreasing light through a solution?

Answer 16

Some reactions create an insoluble solid (precipitate).
Measure the rate at which it makes the solution go cloudy.
You can time when the cross on the bottom disappears.
A light sensor is more accurate than a disappearing cross.

Question 17

What are the four main factors affecting the rate of reaction?

Answer 17

1. Temperature
2. Surface area of solids
3. Concentration (solutions) and/or Pressure (gas)
4. Catalyst

Question 18

How does surface area affect rate of reaction?

Answer 18

Start a camp fire with small pieces of wood not large logs. Small pieces have more surface area than a large log so more area to react with oxygen in the air.
Powder rather than a lump of solid gas so more surface area to react in solution.
SA:V = Surface area to volume ratio
Larger surface area does not make collisions with more energy but does make more collisions without more energy

Question 19

How does temperature affect rate?

Answer 19

A fridge reduces food temperature to slow down rate of reaction (decay). Raising temperature makes particles collide more often and collide with more energy.
Collision theory tells us these increase rate of reaction.
When heated particles move faster so more likely to collide.
Higher temperature means more particles have more activation energy.
Increasing the number of particles exceeding activation energy.
If you increase temperature from room temperature by 10 degrees the rate of reaction will roughly double.

Question 20

Explain how concentration and/or pressure affect rate of reaction?

Answer 20

Increasing concentration means more particles of reactants are moving in the same volume.
So there are more collisions and a faster reaction.
Increasing gas pressure squashes particles closer in the same amount of space.
So more collisions and faster reaction.

Question 21

Explain how temperature affects rate of reaction?

Answer 21

Reaction between 2 solutions
Sodium thiosulfate
Hydrochloric acid

When react make a yellow solid sulphur
Sulphur builds up and obscures underneath the flask

Question 22

How do you calculate the mean rate of reaction?

Answer 22

Total volume of gas made/time taken

Question 23

What apparatus can be used to measure volume of a substance?

Answer 23

Measuring cylinder - acid

Gas syringe - gas

Question 24

Increasing the temperature of a reaction makes….

Answer 24

Particles move faster
Particles collide with more energy
More Frequent successful collisions