Rates Of Reaction

Question 1

What is the rate of reaction?

Answer 1

The speed at which a reactant is used up or a product is made

Question 2

What is the units for the rate of reaction?

Answer 2

g/S or cm^3/s

Question 3

Equations to work out the rate of reaction

Answer 3

Rate of reaction = Amount of reactant used up / time

Rate of reaction = amount of product formed / time

Question 4

What does the collision theory state?

Answer 4

That a chemical reaction can only occur when reacting particles collide with each other with sufficient energy.

Question 5

What is activation energy?

Answer 5

The minimum amount of energy particles must have to react.

Question 6

How do you get a successful collision to happen?

Answer 6

If particles collide with energy greater than the activation energy, a successful collision occurs. The more successful collisions per second, the faster rate of reaction.

Question 7

As the reactants are used up what happens?

Answer 7

The particles collide less often and the reaction slows down.

Question 8

How can we increase the rate of reaction?

Answer 8

Increasing the number of collision per second
Increasing the number of particles
Decreasing the activation energy

Question 9

The effect of particle size on the rate of reaction experiment - what do you use?

Answer 9

Small and large marble chips made out of calcium carbonate. You react it with hydrochloric acid to produce carbon dioxide gas.

Question 10

What is the cotton wool used for in the effect of particle size experiment

Answer 10

To stop any acid from spitting out and allow the carbon dioxide to escape

Question 11

What is the independent and control and dependent and where do they go On a graph?

Answer 11

Independent Variable (the one that is changed - x axis) -
Dependent Variable (the variable being measured - y axis) -
Control Variable  (kept the same) -

Question 12

What is the independent, dependent and control variable in the marble chips experiment?

Answer 12

Independent - the size of chips
Dependent - decreasing mass
Control - weight of chips and concentration of hydrochloric acid.

Question 13

Why might you find a negative mass after adding the content into a conical flask?

Answer 13

Because the carbon dioxide is escaping through the cotton wool

Question 14

How do you work out the average rate of reaction?

Answer 14

Pick a certain time and go up till you get to the line and measure from there. For example, I pick 1min and it goes to 0.47. You do 0.47/1 = 0.47g/min

Question 15

Conclusion for marble chips experiment

Answer 15

Large marble chips - small surface area and small marble chips - large surface area.
If the reactants are smaller, the rate of reaction increases.
Smaller particles of solid have a large surface area so they collide more often and there are more successful collisions per second therefore a faster rate of reaction.

Question 16

What is the independent variable, dependent and control for the effect of concentration experiment

Answer 16

Independent - volume of water
Dependent- volume of gas produced
Control - surface area of Chips and mass of chips

Question 17

What happens to the rate of reaction over time in the effect of concentration experiment?

Answer 17

The rate of reaction slows down and slowly stops. Because the reactants are being used up.

Question 18

Should the volume of carbon dioxide be the same for all the concentrations and why?

Answer 18

Yes because we have the same number of acid particles and so the volume of carbon dioxide should be the same.

Question 19

Which concentration would have the steepest gradient in the effect of concentration experiment?

Answer 19

15cm^3 of acid and 20cm^3 of water because it is the most concentrated and therefore a faster rate of reaction

Question 20

How would you work out the initial rate for the effect of concentration experiment?

Answer 20

The volume of gas produced/ Time

For example at 30seconds the volume was 15 for 30cm^3 water then it would be 15/30

Question 21

Using the collision theory explain why 20cm^3 water has the fastest rate of reaction?

Answer 21

Increasing concentration increases the number of particles per unit volume. There is a greater chance of the particles colliding so more successful collisions per second and therefore the rate of reaction increases.

Question 22

What is the independent, dependent and control variable for the effect of temperatures experiment?

Answer 22

Independent - time taken for cross to disappear

Dependent - volume of sodium thiosulphate and hydrochloric acid

Question 23

When the temperature increases, the rate of reaction increases why? Two methods to explain this

Answer 23

Collision frequency - the particles have more energy so move faster and collide more often
Activation Energy - more particles that have more energy greater than the activation energy equal a higher percentage of collisions that are successful per second.

Question 24

If the pressure of a gas increases why does the rate of reaction increases?

Answer 24

As the pressure increases, there are more particles in a given volume so they collide more often and so there are more successful collisions per second.

Question 25

What is a catalyst?

Answer 25

A substances that increases the rate of a reaction but is chemically unchanged at the end of reaction

Question 26

What is the independent, dependent and control variable of the effect of catalysts experiment

Answer 26

Indepdent - with or without catalyst
Dependent - amount of gas reproches
Control variable - volume of water and hydrogen peroxide

Question 27

If a catalyst is used what happens to the rate of reaction, explain using collision theory.

Answer 27

If a catalyst is used, the rate of reaction increases but the catalyst is unchanged (not used up).
Catalysts provide an alternative route for the reaction with a lower activation energy so more particles have energy greater than the activation energy and more successful collisions per second.

Catalysts reduce energy costs

Question 28

Look at folder for…

Answer 28

Energy profile diagrams for endothermic and exothermic reactions

Question 29

If two experiments contain the same number of particles, how would their graphs look

Answer 29

Graphs will finish at the same heigh as the same amount of products is produced in the end.

Question 30

If two experiments contain half the number particles how will the graph look?

Answer 30

It will produce half amount of product so the graph will finish at half the height

Question 31

Equations for the effect of particle size and effect of catalyst experiment

Answer 31

Effect of particle size - CaCO3 + 2HCl —> CaCl2+ CO2 + H2O

Catalyst - 2H2O2 —> 2H2O + O2

Question 32

How do you prove that a catalyst is not used up?

Answer 32

Filter it off, wash and dry it - the mass should the be the same before and after

Question 33

Name a catalyst and give a use

Answer 33

Finely divided iron - to produce ammonia