C3 Energy calculations

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3.1 Comparing the energy released by fuels

When fuel and food react with oxygen, energy is released in an exothermic reaction.

The energy content of food and fuels can be measured using a calorimeter.

However, these measurements are not accurate because of energy losses, but they are useful for making comparisons.

Q = mc triangle T

Energy released by fuel = mass of water heated in calorimeter X specific heat capacity X rise in temperature

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3.2 Energy transfers in solutions

When a reaction takes place in solution, energy is transferred to or from the solution.

Neutralisation and displacement reactions are both examples of reactions that we can use this technique for:

Q = m x c x TRIANGLE x T

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3.3 Energy level diagrams

We can show the relative difference in the energy of reactants and products on energy level diagrams.

Catalysts lower the activation energy so a greater proportion of reactant particles have enough energy to react.

Bond breaking is endothermic, and bond making is endothermic.

Bond breaking aBsorbs energy, foRming bonds Releases energy.

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3.4 Calculations using bond energies

In chemical reactions, energy must be supplied to break the bonds between atoms in the reactants.

When new bonds are formed between atoms in a chemical reaction, energy is released.

In an exothermic reaction, the energy released when new bonds are formed is less than the energy absorbed when bonds are broken.

In an endothermic reaction, the energy released when new bonds are formed is less than the energy absorbed when bonds are broken.

We can calculate the overall energy change in a chemical reaction using bond energies.

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