- Temperature increase: The temperature of the system increases during the reaction. This is because the energy released by the chemical bonds formed in the products is greater than the energy absorbed by the chemical bonds broken in the reactants.

- Light emission: Some exothermic reactions emit light. This is because the energy released by the chemical bonds formed in the products is so great that it causes the electrons in the atoms to become excited and emit light as they fall back to lower energy levels.

- Heat production: Exothermic reactions produce heat. This is because the energy released by the chemical bonds formed in the products is transferred to the surroundings as heat.

- Gas evolution: Some exothermic reactions produce gases. This is because the energy released by the chemical bonds formed in the products is so great that it causes the molecules to break apart and form gases.

- Sound production: Some exothermic reactions produce sound. This is because the energy released by the chemical bonds formed in the products is so great that it causes the molecules to vibrate and produce sound waves.