Chemistry C3.3

C3 3.1

When fuels react with oxygen, the reaction is always exothermic. The energy given off is in joules, but sometimes given in calories (1 cal = 4.2J).

A calorimeter is used to tell us how much energy a fuel gives off. However, simple calorimeters are not reliable because they consist of a metal can containing water with a thermomiter inside. Therefore, the fuel which is underneath will give off energy, but not all will reach the calorimeter can because energy is given off to surroundings.

However, presuming that it is 100% efficient, you use the following equation to work out how much energy is transferred: amount of energy transferred to water = mass of water, g, x specific heat capacity of water, J/g degrees celcius, x temperature change in degrees celcius.

To compare different energy released you change it to KJ per gram.

To get KJ per mole, you multiply KJ per gram by the relative formula mass of the substance.

C3 3.2

When a reaction occurs, energy transfers either to or from the solution. We can do reactions in insulated containers to reduce energy transfers.

If we measure the change of temperature, we can calculate energy change. In these calculations we assume the solutions are water. This means that 1g of…