Endothermic reactions:

• Absorbs heat energy from the environment

• The environment is getting colder

• Breaking bonds between particles

• Thermal energy → chemical energy

Examples of endothermic reactions:

• The reaction between ethanoic acid (vinegar) and sodium carbonate (baking soda) to produce sodium ethanoate, water, and carbon dioxide

• Electrolysis of water that produces oxygen gas and hydrogen gas

Exothermic reactions:

• Releases heat to the environment

• The environment is getting warmer

• Forming bonds between particles

• Chemical energy → thermal energy

Examples of exothermic reactions:

• Combustion reaction

• Neutralization reaction

The description of endothermic reactions and exothermic reactions:

Exothermic reactions in everyday life:

• Immediate heat packs are used to warm the injured hands, feet, or body parts

• The principle of exothermic reaction applies

• The amount of heat energy released exceeds the amount of heat energy absorbed causing the heating effect to occur

• Combustion is also an example of an exothermic reaction because it releases heat to the environment

Endothermic reactions in daily life:

• Instant cold packs work to cool certain parts of the body

• The principle of endothermic reaction applies

• The amount of heat energy absorbed exceeds the amount of heat energy released causing the cooling effect to occur

• Sweating of the human body is also an example of an endothermic reaction because it absorbs heat from the surface of the body to become water vapor

Example question:

Question 1:

Instant heat packs are often used to warm the  body in cold climates or to treat certain types pf injuries.

When the heat pack is pressed, it becomes hot.

a) What type of reaction occurs when a heat pack is pressed?

b) Explan how this pack works?

Answer 1:

a) Exothermic reaction

b) When the heat pack is pressed, water and magnesium sulfate salt will mix. The reaction that occurs when a salt of magnesium sulfate dissolves in water releases heat energy.

Question 2:

The following bar chart shows data from an experiment that studied temperature changes in reactions A and B.

a) Between reactions A and B, which is an exothermic reaction and which is an endothermic reaction?

b) Give an example of an exothermic reaction and an example of an endothermic reaction in everyday life.

Answer 2:

a) Reacion A is an endothermic reaction and reaction B is an exothermic reaction.

b) Example of exothermic reaction: Combustion of water and sodium hydorxide

Example of endothermic reaction: Reaction between water and ammonium chloride