Section 15 - Heat Energy Changes In Chemical Reactions

Question 1

How is energy most often transferred?

Answer 1

By heating

Question 2

What is exothermic?

Answer 2

Energy transferred from stores of energy in chemical bonds to surroundings

Question 3

What is endothermic?

Answer 3

Energy is transferred from the surroundings to stores of energy in chemical bonds

Question 4

How can you model the energy change during a chemical reaction?

Answer 4

Reaction profiles

Question 5

What do reaction profiles show?

Answer 5

Energy stored in bonds is represented as a horizontal line, greater energy stored is the higher line

Question 6

what does an exothermic reaction profile look like?

Answer 6

|reactants
|———
|             |energy given out 
|             |\_\_\_\_\_\_\_
|             Products
|\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

Question 7

What does an endothermic reaction profile look like?

Answer 7

|               Products
|               \_\_\_\_\_\_\_\_\_
|               | energy given out 
|\_\_\_\_\_\_\_\_|              
| reactants                          
|\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

Question 8

During an exothermic reaction, what happens to the stored thermal energy in a solution?

Answer 8

The stored thermal energy increases

Question 9

What happens to the stored thermal energy in a solution during an endothermic reaction?

Answer 9

It decreases

Question 10

So if a temperature increases, what reaction has taken place?

Answer 10

Exothermic

Question 11

What happens in a precipitation reaction?

Answer 11

An insoluble product forms two solutions

Question 12

What type of reaction is precipitation? Endo of exo?

Answer 12

It’s both, endo and exothermic

Question 13

What 2 types of reaction are always exothermic?

Answer 13

Neutralisation and displacement

Question 14

What is a neutralisation reaction?

Answer 14

The reaction between an acid and a base (BASHO)

Question 15

What is a displacement reaction?

Answer 15

The reaction between metal and a compound of less reactive metal, or between halogen and a compound of less reactive halogen

Question 16

What reaction is taking place when salt dissolves in water?

Answer 16

Exo or endothermic depending on the salt

Question 17

How does putting a polystyrene cup into a beaker keep the cup warm?

Answer 17

The air trapped between the cup and beaker reduces energy transfers by heating, to and from the surroundings

Question 18

Which type of reactions have low activation energies and start as soon as the reactants are mixed?

Answer 18

Precipitation and neutralisation

Question 19

Do combustion reactions have higher or lower activation energies?

Answer 19

Higher activation energies

Question 20

How do you model activation energy in a reaction profile?

Answer 20

By drawing a hump between the reactants and products lines

Question 21

If a substance has a high activation energy, what does it need at the start?

Answer 21

It need energy from a flame or spark

Question 22

What happens to bonds during chemical reactions?

Answer 22

Reactants break and new bonds are formed to make th eproducts

Question 23

What does BENDO MEX stand for?

Answer 23

Breaking endothermic and Making exothermic

Question 24

Why is endothermic breaking bonds?

Answer 24

Because energy is transferred to the reactants to break their bonds

Question 25

Why is making bonds exothermic?

Answer 25

Because energy is transferred to the surroundings as bonds form

Question 26

When is a reaction endothermic?

Answer 26

If less energy is given out making bonds that is needed to break the

Question 27

When is a reaction exothermic?

Answer 27

When more energy is given out to make bonds than energy it takes to break them

Question 28

What is the energy called that is needed to break one mole of a covalent bond?

Answer 28

Bond energy

Question 29

What is bond energy measured in?

Answer 29

Kilojoules per mole (KJ/mole or kJ mole-1)

Question 30

If an equation to find the energy change gives you a negative answer, is it an exothermic or endothermic reaction?

Answer 30

Exothermic