Energy changes during chemical reactions

1. Understanding Energy in Reactions

• Chemical reactions involve energy changes as reactants form products.
• Reactants (left side of equation) → Products (right side of equation).
• Energy is absorbed or released during bond breaking and bond formation.

2. Steps in a Chemical Reaction

✅ Step 1: Energy is needed to break bonds in reactant molecules.

✅ Step 2: The particles enter a high-energy activated state and collide.

✅ Step 3: Energy is released as new bonds form to create products.

• Exothermic reactions release energy.
• Endothermic reactions absorb energy from the surroundings.

3. Types of Energy Changes in Reactions

Term	Definition
Heat of Reaction $(ΔH)$	The energy absorbed or released during a reaction.
Activation Energy $(Ea)$	The minimum energy required for a reaction to start.
Exothermic Reaction	Energy is released, making surroundings warmer ($ΔH$ is negative).
Endothermic Reaction	Energy is absorbed, making surroundings cooler ($ΔH$ is positive).

4. Key Takeaways

✅ Breaking bonds requires energy (endothermic).

✅ Forming bonds releases energy (exothermic).

✅ Activation energy $(Ea)$ is needed to start a reaction.

✅ The overall heat of reaction $(ΔH)$ determines whether a reaction is exothermic or endothermic.