🌡️ Thermodynamics: Exo vs Endo Reactions
Cambridge IGCSE Chemistry (0620) — Papers 2, 3 & 4 Style
15
Questions
30
Total Marks
3
Sections
⚡ The Core Rule of Thermodynamics:
Exothermic = transfers thermal energy to surroundings → temperature rises → ΔH is negative | Endothermic = takes in thermal energy from surroundings → temperature falls → ΔH is positive
Define an exothermic reaction.
Define an endothermic reaction.
What does it mean when ΔH is negative (ΔH < 0)?
What does it mean when ΔH is positive (ΔH > 0)?
In terms of bond breaking and bond making, explain why exothermic reactions release energy.
A student dissolves ammonium chloride (NH₄Cl) in water. The temperature drops from 20°C to 12°C. State the type of reaction and explain why.
When magnesium ribbon is added to hydrochloric acid, the test tube becomes very hot. State the type of reaction occurring.
A student mixes two solutions. The thermometer initially reads 22°C and after mixing reads 35°C. Identify the type of reaction and state the temperature change (ΔT).
The diagram shows an energy level diagram. The products are at a HIGHER energy level than the reactants. Is this reaction exothermic or endothermic? Explain.
A hand warmer contains iron powder and is activated by shaking. After shaking, the pack becomes warm to the touch. State and explain the type of energy change occurring.
Is the combustion of methane (CH₄) exothermic or endothermic? Write the word equation.
Is thermal decomposition of calcium carbonate (CaCO₃) exothermic or endothermic? Explain why heat must be continuously supplied.
Neutralisation of hydrochloric acid with sodium hydroxide produces a temperature rise. State whether this is exothermic or endothermic and write the ionic equation.
Photosynthesis uses light energy to convert carbon dioxide and water into glucose and oxygen. Is photosynthesis exothermic or endothermic?
A student burns ethanol (C₂H₅OH) in a spirit lamp to heat water. The water temperature rises by 15°C. (a) State whether combustion of ethanol is exothermic or endothermic. (b) Explain why the water temperature rises.
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