3.1 EnergeticsEdexcel IGCSE Chemistry: Flashcards

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Define an exothermic reaction.

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Define an exothermic reaction.: A reaction that transfers heat energy to the surroundings, so the surrounding temperature increases.
Define an endothermic reaction.: A reaction that takes in heat energy from the surroundings, so the surrounding temperature decreases.
Give an example of an exothermic reaction.: Combustion, neutralisation, or most oxidation reactions.
Give an example of an endothermic process.: Thermal decomposition, or dissolving certain salts such as ammonium nitrate.
State the equation used to calculate heat energy change from calorimetry data.: Q = mcT, where m = mass, c = specific heat capacity, T = temperature change.
What is the specific heat capacity of water used in calculations?: 4.2 J/g°C.
How is molar enthalpy change (ΔH) calculated from Q?: ΔH = Q ÷ number of moles of the specified substance.
What sign does ΔH have for an exothermic reaction?: Negative, because energy is released.
What sign does ΔH have for an endothermic reaction?: Positive, because energy is absorbed.
On an energy level diagram, how do products compare to reactants for an exothermic reaction?: Products have lower energy than reactants.
On an energy level diagram, how do products compare to reactants for an endothermic reaction?: Products have higher energy than reactants.
Is bond breaking exothermic or endothermic?: Endothermic — energy must be put in to break bonds.
Is bond making exothermic or endothermic?: Exothermic — energy is released when bonds form.
How is the overall enthalpy change of a reaction calculated using bond energies?: ΔH = (total energy to break bonds in reactants) − (total energy released making bonds in products).