7.1-7.3: Energetic of a Reaction and Energy in Reactions

exothermic reaction

During a(n) ________, more energy is energy is given out when new bonds are made than the energy taken in to break bonds.

symbol ΔH

The ________ (delta H) is used to show the change in heat energy.

new bonds

More energy is released when ________ are formed than energy required to break the bonds in the reactants.

H

________ is the symbol for enthaply, which is a measure of the total heat of reaction of a chemical reaction.

chemical reaction

During a(n) ________ there is always an energy change.

endothermic reaction

Therefore a(n) ________ has a positive ΔH value, which is shown on the energy level diagrams and in calculations.

What do the terms exothermic and endothermic mean?

Endothermic - a reaction that takes in heat energy from the surroundings.
Exothermic - a reaction that gives out energy to the surroundings.

Give an example of a type of reaction that is exothermic.

Combustion & Neutralisation

Give an example of an endothermic reaction

Thermal decomposition & Photosynthesis

In terms of bond energies, what happens during a chemical reaction? Describe exothermic and endothermic reactions in terms of bonds breaking / making

Energy is needed to break bonds and is released when bonds are made.
Exothermic: Energy released from making bonds is greater than the energy used to break bonds.
Endothermic: Energy required to break bond is greater than the energy released when making bonds.

What is a reaction profile?

A graph which shows the relative energies of reactants and products, as well as the activation energy of the reaction

How can the energy change of a reaction be calculated from bond energies?

Energy change (kJ mol-1) =
Total energy of bonds broken - total energy of bonds made

If the energy change of a reaction is negative, is the reaction exothermic or endothermic?

Exothermic
Energy has been lost to the surroundings

Fill in the gap: ‘Fuels are burned to release ____ ____’

Heat energy

Which colourless gas can be used as a fuel?

Hydrogen

What is a fuel cell?

A cell that continually produces a voltage as long as it is supplied with oxygen and a fuel (like hydrogen).

What are the advantages of fuel cells?

No pollution produced
- Produce more energy than an alternative
fuel like petrol
- Continuous process as long as fuel is
supplied