Exo and Endo Reactions
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26 Terms
Q: What is an exothermic reaction?
A: A reaction that releases energy to the surroundings. ΔH is negative.
Q: What is an endothermic reaction?
A: A reaction that absorbs energy from the surroundings. ΔH is positive.
Q: What does ΔH represent?
A: The enthalpy change of a reaction, or the heat energy transferred at constant pressure.
Q: What is the unit of molar enthalpy change?
A: kJ mol⁻¹.
Q: Why is an exothermic reaction negative ΔH?
A: The system loses energy to the surroundings, so the products have lower enthalpy than the reactants.
Q: Why is an endothermic reaction positive ΔH?
A: The system gains energy from the surroundings, so the products have higher enthalpy than the reactants.
Q: What happens to energy when bonds are broken?
A: Energy is absorbed.
Q: What happens to energy when bonds are formed?
A: Energy is released.
Q: What is activation energy?
A: The minimum energy required for reactant particles to reach the transition state and react.
Q: Does a catalyst change ΔH?
A: No. A catalyst lowers activation energy but does not change the overall enthalpy change.
Energy diagrams
Exothermic: Products are lower in energy than reactants.
Endothermic: Products are higher in energy than reactants.
Activation energy: Energy needed to start the reaction.
ΔH: Overall energy difference between reactants and products.