Topic 5-Energy Changes Flashcards
What is an exothermic reaction?
An exothermic reaction is one which transfers energy to the surroundings usually by heating. This is shown by a rise in temperature.
What is an example of a exothermic reaction?
Combustion (burning of fuels).
Neutralisation reactions.
Oxidation reactions.
What are everyday exothermic reactions?
Hand warmers use exothermic oxidation of iron in air to release energy.
Self heating cans of hot chocolate and coffee rely on exothermic reactions between chemicals in their bases.
What is an endothermic reaction?
It takes energy in from the surroundings. This is shown by a fall in temperature.
What is an example of an endothermic reaction?
Thermal decomposition.
Citric acid and sodium hydrogencarbonate.
What are everyday endothermic reactions?
They are in sports injury packs. The chemical reactions allows the pack to become instantly cooler without having to put it in the freezer.
How can you measure energy transfer? (practical)
Takinf the tenperature of the reagents mixing them in a polystrene cup and measuring the temperature of the solution at the end of the reaction.
To reduce energy lost to the surroundings by wrapping the cup in cotton wool for insulation and putting a lid on to reduce energy lost by evaporation.
Describe how you can test the effect of acid concentration on the energy released in a neutralisation reaction between hydrochloric acid and sodium hydroxide?
Place a known amount of hydrochloric acid and sodium hydroxide in separate beakers.
Place the beakers in a water bath set to 25C until they are both the same temperature.
Add hydrochloric acid and sodium hyroxide to a polystyrene cup.
Take the temperature of the mixture every 30 seconds amd record the highest temperature.
Change the concentraction of hydrochloric acid and repeat the experiment.
What type of process is bond breaking?
Endothermic process.
What type of process is bond formation?
An exothermic process.
