# CHEMISTRY- OCR B - SALTERS - DEVELOPING FUELS

- Created by: lois ghost
- Created on: 01-04-12 19:02

**Developing Fuels:**

**calculations from equations...**

any numbers in front of an element or compound in an equation state the number of moles in the reaction.

working out masses:

1. write a balanced equation, then underline the substances whose mass you were given and mass you want to find out.

2. indicate the number of moles involved.

3. calculate the masses (Mr/Ar x moles)

4. convert to the mass given in the equation (using the first mass to divide then multiplying by the mass given in the equation)

5. repeat this step for the unknown, dividing it by the first mass then multiplying it by the given mass in the question.

6. now write down your answer.

working out volumes of gases:

* remember 1 mole of a gas is always 24 dm^3 at room temperature and pressure (25^oC and 1 atm.)

1. write a balanced equation, then underline the substances whose volume you were given and volume you want to find out.

2. indicate the number of moles involved.

3. calculate the volumes (24 dm^3 x moles)

4. convert to the volume given in the equation (using the first volume to divide then multiplying by the volume given in the equation)

5. repeat this step for the unknown, dividing it by the first volume then multiplying it by the given volume in the question.

6. now write down your answer.

working out with both mass and volume:

1. write a balanced equation, then underline the substances whose mass/volume you were given and mass/volume you want to find out.

2. indicate the number of moles involved.

3. calculate the mass/volume (Mr/Ar x moles or 24dm^3 x moles)

4. convert to the mass/volume given in the equation (using the first mass/volume to divide then multiplying by the mass/volume given in the equation)

5. repeat this step for the unknown, dividing it by the first mass/volume then multiplying it by the given mass/volume in the question.

6. now write down your answer.

working with enthalpy changes:

1. write a balanced equation, then underline the substances whose masses/volumes you were given and the enthalpy change you were given.

2. indicate the number of moles involved.

3. calculate the masses (Mr/Ar x moles)

4. convert to the mass/volume given in the equation (using the first mass/volume to divide then multiplying by the mass/volume given in the equation)

5. repeat this step for the unknown, dividing it by the first mass/volume then multiplying it by the given mass/volume in the question.

6. now write down your answer.

* The **enthalpy change of combustion** tells you the amount of energy released when 1 mole of a fuel is completely burnt.

**enthalpy and entropy...**

enthalpy:

- an exothermic reaction gives out energy from the system to the surroundings. the temp. of the surroundings increases- delta H is -ve

- an endothermic reaction takes in energy from the surroundings. the temp. of the surroundings decreases - delta H is +ve

- the **standard enthalpy change of combustion**, delta Hc, is the enthalpy change when one mole…

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