Chemical Energetics

Question 1

Exothermic

Answer 1

An exothermic reaction gives out heat.

The total chemical energy of the reactants is larger than the products.

This difference in energy is transferred to surroundings as heat.

Question 2

Endothermic

Answer 2

An endothermic reaction takes in heat.

The chemical energy of the reactants is smaller than the products so this

difference in energy is transferred from the surroundings to the chemicals.

Question 3

Bond breaking

Answer 3

Endothermic process. Energy must be “taken in” to break bonds apart.

Question 4

Bond making

Answer 4

Exothermic process. Energy (heat) is released when this happens.

Question 5

Hydrogen fuel cell Anode

Answer 5

At the anode, hydrogen molecules lose electrons to form ions in the electrolyte

H2 - 2e- = 2H

Question 6

Hydrogen fuel Cathode

Answer 6

At the cathode, oxygen gains electrons:

O2 + 2H2O + 4e- = 4OH-

Question 7

Hydrogen cell is a ___ reaction

Answer 7

The formation of water is essentially an exothermic reaction (i.e. energy is released).

When hydrogen reacts with oxygen to form water in a fuel cell, electrical energy is produced.

2H2 + O2 = 2H2O