Energetics - (CCEA)Endothermic reactions

When a chemical reaction occurs, energy is transferred to, or from, the surroundings. An exothermic reaction releases heat to the surroundings and an endothermic reaction absorbs heat from the surroundings.

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Endothermic reactions

An reaction takes in energy from its surroundings. The temperature of its surroundings decreases.

The reaction between sodium hydroxide and hydrochloric acid is exothermic.

The reaction between sodium carbonate and ethanoic acid is endothermic.

An exothermic reaction between dilute sodium hydroxide and hydrochloric acid.

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1. Sodium hydroxide solution is poured into a beaker of hydrochloric acid. Inside is a thermometer showing room temperature.
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2. The beaker now contains sodium chloride and water. The thermometer shows a rise in temperature. The neutralisation reaction is exothermic.
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3. Sodium carbonate powder is tipped into a beaker of ethanoic acid, which contains a thermometer showing room temperature.
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4. The beaker now contains sodium ethanoate, water and carbon dioxide. The thermometer shows a fall in temperature. This is an endothermic reaction.

Reactions and temperature changes

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