Chemical Energetics

electric circuit

The flow of the electrons, through the ________, from the cathode to the anode generates a current.

combustion process

A(n) ________ requires the presence of a fuel, oxygen and heat.

Heat energy

________ is absorbed from the surroundings.

exothermic reaction

Burning fuels to form oxides is a(n) ________.

Fuel

________: substance that can be used as a source of energy.

overall heat energy value

If ________ is positive, reaction is endothermic.

Energy level diagrams

________ show the relative energies of the reactant and product.

Heat energy

________ is released into the surroundings.

overall heat energy value

If ________ is negative, reaction is exothermic.

Energetics of a Reaction

Chemical reactions involve a transfer of energy between the system (the chemical reaction) and its surroundings

Activation energy

the minimum energy required for the reaction to take place

Fuel

substance that can be used as a source of energy

The product is water

2H2 + O2 → 2H2 O

4H+ + O2 + 4e

→ 2H2 O

A good fuel is:

Cheap

Available in large quantities

Liquid at room temperature

Have high efficiency (produce a large amount of energy)

Does not produce polluting gases

Advantages of Hydrogen fuel cells

Releases a lot of energy

Does not produce pollutants

Renewable and abundant

Disadvantages of hydrogen fuel cells

Difficult to transport as it is a gas at room temperature

Forms explosive mixture with air when stored under pressure

Is expensive to produce (requires a lot of energy)

exothermic reaction

Heat energy is released into the surroundings

Bond making reactions

Surrounding temperature increases

endothermic reaction

Heat energy is absorbed from the surroundings

Bond breaking reactions

Surrounding temperature decreases

Product(s) of hydrogen fuel cell

Water (ONLY)