Chapter 7: How far? How fast?

Question 1

Define chemical bonds:

Answer 1

Forces of attraction between atoms or ions

Question 2

Define endothermic process:

Answer 2

a process that breaks bonds and takes heat in.

Negative heat of reaction.

Question 3

Define exothermic process:

Answer 3

a process that makes bonds and gives heat out.

positive heat of reaction.

Question 4

Define heat of reaction:

Answer 4

the energy change going from reactants to products in a chemical reaction.

Question 5

Define bond energy:

Answer 5

the average value obtained for a particular bond.

Question 6

What is an energy level diagram?

Answer 6

a representation of what happens during a reaction in terms of energy.

Question 7

How do you calculate bond energies?

Answer 7

energy to break bond - energy to form bond

Question 8

Define activation energy:

Answer 8

the minimum kinetic energy that particles must have before a reaction can happen. (energy needed to break old bonds before new ones can be formed)

Question 9

define the rate of a chemical reaction:

Answer 9

the time taken for a specific quantity of reactant to be used up or for the product to be formed.

Question 10

How do you calculate the rate of reaction?

Answer 10

change in quantity of products/ time taken for the change

also calculated from the tangent of a graph

Question 11

How to calculate the mean rate of reaction?

Answer 11

quantity of product formed/ time taken

Question 12

Factors that affect rate of reaction:

Answer 12

• temperature
• concentration
• surface area of reactant
• presence of catalyst

Question 13

Define catalyst:

Answer 13

a substance that increases the rate of a chemical reaction and remains chemically unchanged at the end of the reaction.
provides an alternative pathway for a reaction.

Question 14

What is a photochemical reaction?

Answer 14

a reaction that is activated by the absorption of light which transfers energy to the reactants that then react.

Question 15

define a reversible reaction:

Answer 15

a reaction that can be reversed if we change the conditions that the reactions are in.

Question 16

define a forward reaction:

Answer 16

represented by a chemical equation and by convection the reaction goes from left to right.

Question 17

define chemical equilibrium:

Answer 17

when in an enclosed system both the forward and backward reactions are equal and therefore the products formed are used up as soon as they are made.

Question 18

State Le Chatelier’s principle:

Answer 18

when a system’s conditions change the system will do something opposite to try and come back to equilibrium. ( the equilibrium therefore shifts )

Question 19

Conditions of the Haber process:

Answer 19

• N2 and H2 are mixed in the ration 1:3
• optimum temperature (450) and pressure (200 atmospheres) is applied
• a catalyst of finely divided iron is used
• ammonia is condensed out and H2 + N2 are reused

Question 20

State the collision theory:

Answer 20

a chemical reaction can only take place when the reacting particles collide with each other and have sufficient energy.