Topic 1- Rates

Question 1

How can reaction rate be calculated?

Answer 1

Change/time interval

1/time (relative rate)

Question 2

What are rates of reactions affected by? (5)

Answer 2

Concentration 
Pressure
Particle size
Temperature 
Catalysts

Question 3

What is the collision theory?

Answer 3

States that reactants must collide with the correct geometry and possess a min energy(activation energy) before a successful reaction occurs

Question 4

What is temperature?

Answer 4

A measure of the av kinetic energy of the particles of a substance

Question 5

What is the activation energy?

Answer 5

Is the min kinetic energy required by colliding particles before reaction will occur

Question 6

What are energy distribution diagrams used for?

Answer 6

To explain the effect of changing temp on the kinetic energy of particles

Question 7

Why does increasing the concentration increases the rate?

Answer 7

Increases the number of particles in a given vol which means there are more successful collisions

Question 8

Why does increasing the pressure of a gas increase the rate?

Answer 8

Increases the conc of the gas which increase the no of particles in a given volume which means there are more successful collisions

Question 9

Why does decreasing the particle size increase the rate?

Answer 9

Increases the surface area of the reactant, this increases the no of possible collisions, therefore the rate of successful collisions will increase

Question 10

Why does an increase in temperature increase the rate?

Answer 10

Because the av kinetic energy of the colliding particles increases, thus means that more particles collide with the Ea resulting in more successful collisions

Question 11

What is a catalyst?

Answer 11

They increase the rate of a reaction by providing an alternative reaction pathway with a low activation energy

Question 12

What is the activated complex?

Answer 12

A high energy unstable arrangement of atoms it is formed at the top of the activation energy barrier

Question 13

Why do reaction rates have to be controlled? (2)

Answer 13

If they are too low=not economically viable

If they are too high= risk of thermal explosion

Question 14

What do negative catalysts do?

Answer 14

They decrease the rate by increasing the activation energy

Question 15

What is a heterogeneous catalyst? Give example

Answer 15

They exist in different state to reactants. They are solids that catalyses reactions between reactants that are gases, liquids or in solution. e.g. which catalyses the reaction between hydrogen and nitrogen in the Haber process.

Question 16

What is a homogeneous catalyst? Give example

Answer 16

They exist in the same state to reactants. E.g. Enzymes are homogeneous catalysts as they are found in aqueous solution and the reactants are also in aqueous.

Question 17

What effect does a catalyst have on enthalpy change?

Answer 17

no affect

Question 18

How do you calculate the overall enthalpy change of a reaction?

Answer 18

Energy of the products - Energy of the reactants

Ep-Er

Question 19

When new bonds are formed, is that an exothermic or endothermic reaction?

Answer 19

Exo

Question 20

What are the 3 steps of catalysis occurring on the active sites of heterogeneous catalysts?

Answer 20

Step 1- adsorption ( molecules of one or both reactants form both with the catalyst, the weakens the bonds with molecules)
Step 2- Reaction (the molecules react on the catalyst surface.)
Step 3- Desorption (the product molecules leave the catalyst and the vacant site can be used again)

Question 21

What is an active site?

Answer 21

The points on the surface of the solid catalyst were the reactant molecules become absorbed

Question 22

How do you increase the number of active sites?

Answer 22

A thin layer of the catalyst is often coated onto beads to increase the surface area upon which the reaction can take place.