Energy Changes in Chemical Reactions

Question 1

Define exothermic

Answer 1

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

Question 2

Define endothermic

Answer 2

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

Question 3

In a reaction profile, which way would the arrow point for an exothermic reaction

Answer 3

Down (energy released)

Question 4

In a reaction profile, which way would the arrow point for an endothermic reaction

Answer 4

Up (energy taken in)

Question 5

How can you determine if a reaction is endothermic or exothermic using temperature?

Answer 5

Exothermic - Temperature increases
Endothermic - Temperature decreases

Question 6

Name 2 exothermic reactions

Answer 6

Neutralisation (reaction between an acid and a base)
Displacement (reaction between a metal, and a compound of less reactive metal OR between a halogen and a compound of a less reactive halogen)

Question 7

How can you add activation energy to a reaction profile?

Answer 7

See notes

Question 8

What happens during endothermic reactions, in terms of bonds?

Answer 8

Energy is transferred to reactants to break their bonds, so bond breaking is endothermic

Question 9

What happens during exothermic reactions, in terms of bonds?

Answer 9

Energy is transferred to the surroundings as bonds form, so bond making is exothermic

Question 10

Name all of the bond energies of: C-O, C-H, H-H, O-H, O=O, C=O

Answer 10

C-O: 358
C-H: 413
H-H: 436
O-H: 464
O=O: 498
C=O: 805

Question 11

How do you calculate energy changes in reactions?

Answer 11

Energy of bonds in - Energy of bonds out

If the answer is negative, the reaction is exothermic as bonds are being made
If the answer is positive, the reaction is endothermic as bonds are being broken

Question 12

What happens, in terms of temperature, during exothermic reactions?

Answer 12

More heat energy is released in forming bonds in the products than is required in breaking bonds in the reactants (so, temperature increases)

Question 13

What happens, in terms of temperature, during endothermic reactions?

Answer 13

Less heat energy is released in forming bonds in the products than is required in breaking bonds in the reactants (so, temperature decreases)