Exothermic and Endothermic reactions Flashcards
The amount of energy in the universe stays the same. But why ?
1) Chemicals store a certain amount of energy - and diff chemicals store diff amounts
2) If the product of a reaction show more energy than the original reactants, then they must be taken in The diff in energy between the product and reactants from the surroundings during the reaction.
3) But if they store less, then the excess energy was transferred to the surroundings during the reaction.
4) The overall amount of energy don’t change. This is because energy is conserved in reactions - it can’t be created or destroyed, only moved around. This means the amount of energy in the universe stays the same.
What is an exothermic reaction
- include examples
One which transfers energy to the surroundings, usually by heating. This is shown by the rise in temp.
The best example - burning fuels ( Combustion ) which gives out a lot of energy.
Neutralisation reactions are also exothermic, Many oxidation reactions are exothermic. For example: adding sodium to water releases energy = exothermic. The reaction releases energy and the sodium moves about on the surface of the water as it is oxidised.
Exothermic reactions everyday use
- Hand warmers use the exothermic oxidation of iron in air to release energy
- self heating cans of coffee rely on exothermic reactions between chemicals in their bases
What is an endothermic reaction
- include examples
One which takes in energy from surroundings. This is shown by fall in temperature.
Less common but include
- reaction between citric and sodium hydrogencarbonate
- Thermal decomposition - Heating calcium carbonate causes it to decompose into calcium oxide and Carbon dioxide
CaCO3 ( + HEAT ) –> CO2 + CaO
endothermic reactions everyday use
sports injury packs- the chemical reaction allows the pack to become instantly cooler w/o having to put it in the freezer
