Heat Energy Changes Flashcards

All 7 cards in this deck

What is an exothermic reaction or change?

One in which heat energy is given out (released) to the surroundings.

What is an endothermic reaction or change?

One in which heat energy is taken in (absorbed) from the surroundings.

Name four types of change that are accompanied by heat energy changes.

Salts dissolving in water, neutralisation reactions, displacement reactions and precipitation reactions.

How is the heat energy change of a reaction in solution measured?

e.g. neutralising dilute acid with alkali in a polystyrene cup

By the temperature change: record the starting temperature, mix and stir, then record the highest (or lowest) temperature reached.

When measuring a temperature change in a polystyrene cup, why is the cup packed in cotton wool inside a beaker and covered with a lid?

To reduce heat transfer between the mixture and the surroundings: the cotton wool insulates the cup and the lid cuts heat lost by evaporation, so the measured temperature change is more accurate.

Does dissolving a salt in water always make the temperature rise?

No. It depends on the salt: some dissolve exothermically (temperature rises) and others endothermically (temperature falls).
e.g. anhydrous magnesium sulfate warms the water; ammonium nitrate cools it.

How can a thermometer show whether a reaction in solution is exothermic or endothermic?

If the temperature of the mixture goes up, heat has been given out (exothermic); if it goes down, heat has been taken in (endothermic).