What are fuels?
- The petrol tank empties as you make your way up the motorway in the car. Each explosive combustion in the engine burns up a carefully measured quantity of fuel with oxygen from the air.
- Boiling rice over a gas flame in the kitchen uses up the gas, a fuel transported to your home through a pipe.
- Frying bacon over an electric ring can also be driven by burning a fuel – but the burning is not in your house. The fossil fuel powered generating station may be burning coal several tens of kilometres away, so long as it is connected to your home by electrical wires. These wires form part of an electrical circuit, making the outcome of burning that fuel available to you in your home.
- Thinking hard draws on the food fuel eaten at breakfast time, as does the brisk walk to catch the bus to school in the morning. This kind of burning (in the human body) is less rapid, but still depends on combining a fuel with oxygen.
In each of these examples, the fuel gets used up as the different jobs are done, and this fits in well with the idea that you cannot get something for nothing. You can only burn a fuel once. Once the chemicals have combined with oxygen, that's it.
As any Yorkshire person will tell you:
You can never get owt for nowt!.
Here's an example where fuel is burnt, and there is an energy change
You need to identify carefully what change you're discussing.