Define Exothermic Reaction.

Introduction

Exothermic reaction is the chemical reaction basically characterized by showing release of energy in the form of heat or light. For example, when we rub matchstick on the matchstick box it releases light and heat. This reaction shows the energy release in both heat and light form. The degenerate form of energy in an exothermic reaction gets transmitted to the adjoining environment.

Thus, the enthalpy (enthalpy is used to measure the heat content during evaluation of the energy change) change in exothermic reactions shows negative values. In exothermic reactions, there is a decrease in the enthalpy of system. As the exothermic reaction discharges heat energy into the surroundings, there is increase in the surrounding temperature as it gains heat from the system.

Figure 1: Illustration of exothermic reaction

Exothermic Reaction

On combustion of methane gas, heat releases forming exothermic reaction. The methane combustion releases heat energy of 890.4 kJ. This reaction shows two ways balanced equation. The amount of released heat is written in reaction at product side. On another side the ΔH value with negative sign can be written (-890.4 kJ).

$$\mathrm{CH_4 (g) + 2O_2 (g)\:\rightarrow\:CO_2 (g) + 2H_2O (l) + 890.4 \:kJ\:(Heat\:produces)}$$

Energy diagram of Exothermic Reaction

In exothermic reaction, bindings between atoms of product molecules are strong bond and consist of higher bond energy as compared to reactants. The product energy is less than the reactant energy, thus it shows downward energy slope. Reactants losses its energy and converts to products. The energy release in the form of heat (can also be in the form of light). As we discussed earlier, in exothermic reaction, heat is released to the surrounding from system and gets warmer.

Figure 2: Exothermic reaction diagram

Examples of Exothermic Reactions

Firecracker Firing

The firecracker when gets burst produce lots of noise with heat and light shows an exothermic reaction.

Sodium Acetate precipitation

The reusable hand warmer has a supersaturated sodium acetate compound. If the pack get bends, tiny metal pieces allows the sodium acetate compound to get nucleated or form crystals. The crystal formation and growth shows exothermic process as the hand warmers gets heat up.

Lighting of Candle

Lightning of candle is a continuous reaction in which the wax plays a role of fuel and produces a flame for longer time.

Rusting

The iron metal gets oxidized and forms iron oxide also known as rust shows an exothermic process. Generally no one noticed the temperature change during rusting of iron. The process of rust formation, between the damp air and iron materials discharge lots of heat.

Combustion

The combustion reaction shows exothermic process. For example, burning of fuel like, gas or wood discharge heat to environment and keeps a house or any place warm. We feel warm if we sit near the campfire as it releases heat into the atmosphere during combustion reaction.

Lighting of Bulb

When the electric current passes through bulb, the current causes the reaction in tungsten filament of bulb and produces light and heat hence, shows exothermic reaction.

Dissolution of NaOH

The strong acid and base like sulfuric acid and sodium hydroxide base, when added to water results in discharge of huge amount of heat. Thus, in chemical laboratories always mix the strong acid or base in water, but not water in acid or base as this process can release a huge amount of heat in atmosphere.

Conclusion

Exothermic reaction is a chemical reaction in which the energy releases by system in the form of heat or light into the surrounding. There is the decrease in the value of enthalpy in the final products which indicates with negative value of enthalpy. Due to the release of heat into the surrounding environment the temperature get increases of surrounding.

In exothermic reaction, the bond of product is strong and has high bond energy than reactants. The energy of product is less than that of reactant in exothermic reaction, thus if we plot a graph of exothermic reaction it shows a downward slope of energy.

FAQs

Q1. Define Exothermic reaction.

Ans. Exothermic reaction is a chemical reaction in which the energy of system discharge into the surrounding environment in the form of heat or light.

Q2. What happen when energy of system released in surrounding?

Ans. When the energy of system gets released into the surrounding the temperature of the surrounding gets increased due to release of heat. Also the enthalpy value gets decreases and shows negative value.

Q3. Explain the exothermic reaction in reactant and product of a chemical reaction.

Ans. Exothermic reaction is the chemical reaction in which the bond of the product is strong and has high bond energy than reactants. Also the energy of product is less than the energy of reactant. Reactant lost its energy and converted into the product.

Q4. Select the one which is not exothermic reaction from the below given options.

a)Rusting b) Bursting of crackers 3) Hydrolysis 4) Lightening of candle

Ans. Hydrolysis is not an exothermic reaction. It is an endothermic reaction. In hydrolysis process, water molecule gets reacts with the bond of other molecule to break the molecule in two parts. Thus, the external heat is required to apply to flask for this kind of reaction in laboratory.

Q5. Give an example of exothermic reaction.

Ans. Combustion: The combustion reaction shows exothermic process. For example: Burning of fuel like gas or wood discharge heat to environment that keeps a house or any place warm. We feel warm if we sit near the campfire as it releases heat into the atmosphere with combustion reaction.