Endothermic Reaction Examples in Chemistry

Start with the recap, study the fully worked examples, then use the practice problems to check your understanding of Endothermic Reaction.

This page combines explanation, solved examples, and follow-up practice so you can move from recognition to confident problem-solving in Chemistry.

Concept Recap

A chemical reaction that absorbs energy (usually as heat) from the surroundings, resulting in a decrease in surrounding temperature and a positive enthalpy change (\Delta H > 0).

The reaction needs heat to proceed — you can feel the surroundings get colder as it runs.

Read the full concept explanation →

How to Use These Examples

  • Read the first worked example with the solution open so the structure is clear.
  • Try the practice problems before revealing each solution.
  • Use the related concepts and background knowledge badges if you feel stuck.

What to Focus On

Core idea: Products have more energy than reactants; the extra energy is absorbed from the surroundings.

Common stuck point: \Delta H is positive for endothermic reactions (energy enters the system).

Sense of Study hint: When determining if a reaction is endothermic, check the sign of \Delta H. First look at whether the surroundings cool down (energy absorbed). Then check if the energy diagram shows products higher than reactants. Finally, confirm that \Delta H is positive.

Worked Examples

Example 1

easy
Photosynthesis absorbs energy: 6\text{CO}_2 + 6\text{H}_2\text{O} + \text{energy} \rightarrow \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2. Why is this endothermic?

Solution

  1. 1
    In an endothermic reaction, energy is absorbed from the surroundings because products have higher potential energy than reactants.
  2. 2
    For photosynthesis, the reactants are \text{CO}_2 and \text{H}_2\text{O}; the product is glucose, which stores more chemical potential energy in its bonds.
  3. 3
    Since the system absorbs energy (sunlight) rather than releasing it, the enthalpy change is positive: \Delta H > 0.

Answer

\Delta H > 0 \quad\text{(endothermic — absorbs energy)}
Endothermic reactions absorb energy from the surroundings. Plants use sunlight as the energy input for photosynthesis, storing that energy in the bonds of glucose.

Example 2

medium
An instant cold pack contains ammonium nitrate and water. When the inner bag is broken, the temperature drops from 25°\text{C} to 5°\text{C}. Classify the process and explain.

Example 3

medium
Photosynthesis absorbs 2803 kJ per mole of glucose. Is it endothermic or exothermic? What is the sign of \Delta H?

Practice Problems

Try these problems on your own first, then open the solution to compare your method.

Example 1

easy
Cooking an egg requires continuous heat input. Is this an endothermic or exothermic process?

Example 2

easy
An instant cold pack becomes cold when activated. Is the process inside the pack exothermic or endothermic? Explain.
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Background Knowledge

These ideas may be useful before you work through the harder examples.

chemical reactionenergy