- Comparing the energy released by fuels
- When fuels and food react with oxygen the reactions are exothermic. Different amounts of energy are released by different fuels and foods. The amount of energy released is usually measured in joules, but sometimes values are given in calories (1 cal = 4.2J).
- we can use a calorimeter to measure the amount of energy released when substances burn. The simplest calorimeter is some in a glass beaker or metal can- the temperature rise of the water as the substance burns depends on the amount of energy released.
- The amount of energy transferred to the water can be calculated using the equation: Q=m*c*deltaT where Q=amount of energy transferred in J M= mass of water in g C= specific heat capacity of water J/g'C DeltaT= temperature change in 'C
- Simple calorimeters do not give accurate results for the energy released because much of it is lost to the surroundings. However, results can be used to compare the energy released by differentfuels
- To compare energy released by burning different substances either the energy change in kJ per gram or the energy change in kJ per mole can be used.