How endothermic reaction occurs

Answer 1

Endothermic reactions are chemical reactions that absorb energy from their surroundings, typically in the form of heat. In these reactions, the energy required to break the bonds of the reactants is greater than the energy released when new bonds form in the products. As a result, the overall energy of the system increases, which is why these reactions feel cold to the touch.

Here’s how an endothermic reaction occurs step-by-step:

1. **Reactant Bonds Breaking**: Energy is needed to break the chemical bonds within the reactant molecules. This energy is typically absorbed from the surroundings.

2. **Intermediate State**: The reactants go through a high-energy intermediate state where bonds have been broken but new bonds have not yet formed. This is usually an unstable state and requires the input of energy (activation energy).

3. **Formation of Product Bonds**: As new bonds form to create the product molecules, energy is released, but the amount of energy released is less than the energy absorbed to break the initial bonds.

4. **Net Energy Absorption**: Since the energy absorbed to break bonds is greater than the energy released from forming bonds, there is a net absorption of energy. This energy is taken from the surroundings, leading to a decrease in temperature around the reaction site.

**Characteristics of Endothermic Reactions**:
- They often require a continuous input of energy to proceed.
- The surroundings typically get cooler.
- Examples include photosynthesis in plants, the dissolution of ammonium nitrate in water, and the thermal decomposition of calcium carbonate.

**Thermodynamics Perspective**:
From a thermodynamics perspective, the enthalpy change (ΔH) for an endothermic reaction is positive, indicating that the products have higher energy compared to the reactants.

**Example**:
A common example of an endothermic reaction is the dissolution of ammonium nitrate (\( \text{NH}_4\text{NO}_3 \)) in water:
\[ \text{NH}_4\text{NO}_3 \ (s) \rightarrow \text{NH}_4^+ \ (aq) + \text{NO}_3^- \ (aq) \]
In this reaction, the ammonium nitrate solid absorbs energy from the water to dissolve, which cools down the solution.

In summary, endothermic reactions occur through the absorption of energy, which is needed to break bonds in reactants that exceed the energy released from new bond formation in the products.