Energy Changes Flashcards
1
Q
what is an exothermic reaction
A
- a reaction in which transfers energy to the surroundings usually by heating, shown by a rise in temperature
2
Q
give 2 examples of endothermic reactions
A
- reaction btwn citric acid and sodium hydrogencarbonate
- thermal decomposition (heating CaCO3 causing it to decompose into CaO and CO2)
CaO3 (+HEAT) ==> CO2 + CaO
3
Q
what is an endothermic reaction
A
- a reaction in which takes in energy from the surroundings, shown by a fall in temperature
4
Q
give 2 examples of endothermic reactions
A
- oxidation reactions ie adding sodium to water releases energy and the sodium moves about on the surface of the water as its oxidised
- combustion gives out a lot of energy
5
Q
give an example of an endothermic reaction in everyday life
A
- sports injury packs. the chemical reaction allows the pack to become instantly cooler without havingto put it in the freezer
6
Q
give an 2 examples of an exothermic reaction in everyday life
A
- hand warmers use exothermic oxidation of iron in in air with a salt solution catalyst to release energy
- self heating cans of hot chocolate and coffee which rely on exothermic reactions btwn chemicals in their bases
7
Q
a student prepares a flask containing ethanoic acid & measure its temp 22.5C then adding a solution which is 21C. after 2 mins the temp of the reaction mixture is 28.5*C
is this reaction exotheric or endothermic?
A
exothermic
8
Q
how can you measure the amount of energy released by a chemical reaction.
A
- take the temperature of the reactants by mixing them in a polystyrene cup
- then measure the temp of the solution at the end of th reaction
9
Q
identify the main problem with the method to measure the amount of energy released by a chemical reaction.and how to reduce this
A
- the main problem is the amount of energy lost to the surroundings
- you can reduce this by putting the polystyrene cup into a beaker of cotton wool giving more insulation
- also put a lid on the cup to reduce energy lost by evaporation
