Chemical Energetics

Chemical Energetics

A branch of chemistry dealing with the (heat) energy change that takes place during chemical reactions.

Exothermic or Endothermic?

• Exothermic: A reaction which involves the release of heat energy (temperature of the reaction mixture increases)

• Endothermic: A reaction which involves the intake of heat energy (temperature of the reaction mixture decreases)

• The overall change in energy is called the heat of reaction

Multiple Choice

When wood is burnt to keep us warm. This is an example of an ------------ reaction

• displacement

• exothermic

• endothermic

Multiple Choice

Thermal decomposition is a chemical change that requires strong heating. It is an example of -------------- reactions

• displacement

• exothermic

• endothermic

Multiple Choice

An exothermic change is detected when the temperature ____

• stays the same

• increases

• decreases

Activation energy

The minimum amount of energy needed to start a chemical reaction

Heat of reaction ( ∆H) = energy taken in – energy given out

• For exothermic reactions, ∆H is negative; Eout > Ein

• For endothermic reactions, ∆H is positive; Ein > Eout

Multiple Choice

The energy taken into a reaction is higher than the energy given out, when the reaction is _____

• endothermic

• exothermic

Multiple Select

The ∆H of a reaction refers to: (check all that apply)

• energy gained

• energy released

• the overall change in energy

• the heat of reaction

Exothermic Reactions

Products are more stable than the reactants (have less internal energy).

Eout > Ein

Endothermic Reactions

Reactants are more stable than the products. Ein > Eout

Multiple Select

Choose the examples of exothermic reactions

• dehydration

• displacement

• nuclear reactions

• combustion

• photosynthesis

Fuels

Substances burnt to produce energy

Multiple Select

What do you think makes a good fuel? check all that apply

• cheap

• readily available

• easy to ignite (burn)

• doesn't cause pollution

• easy to transport

Characteristics of a good fuel:

• Cheap

• Releases a large amount of energy/unit mass

• Doesn't cause pollution

• Easy to ignite

• Easy to transport and store

• Available in large quantities

Hydrogen as a fuel

Nuclear Energy

Do the benefits outweigh the risks?

Nuclear Reactors

• In nuclear reactors, U­235 undergoes fission which produces a large amount of energy. 

• This energy is used to boil water.

• The resulting steam is used to drive turbines which in turn generate electricity.