Explain what the sign of ΔH tells you about the energy changes involved in the reaction.

If ΔH is positive, energy is transferred from the surroundings to the system. The temperature of the surroundings decreases and the reaction is endothermic.


If ΔH is negative, energy is transferred from the system to the surroundings. The temperature of the surroundings increases and the reaction is exothermic.

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What is enthalpy change a measure of?

The amount of heat energy absorbed or released during a reaction.

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What sign is used to denote standard conditions?

⦵

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What are the typical units for enthalpy change?

kJ mol-1

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What is the standard pressure in kPa?

101 kPa


Standard pressure can also be 101 kPa or 1 atm.

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What is the standard temperature in °C?

25°C


Standard temperature is also 298 K. 

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What is standard state?

The physical state of a substance under standard conditions (of 25°C and 101 kPa).

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How is standard enthalpy change of formation ΔfH⦵ defined?

The enthalpy change when one mole of a compound is formed from its elements under standard conditions.

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How is standard enthalpy change of combustion ΔcH⦵ defined?

The enthalpy change when one mole of a substance reacts completely with oxygen under standard conditions.

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How is standard enthalpy change of neutralisation ΔH⦵neut defined?

The energy change that accompanies the neutralisation of an acid and an alkali to form one mole of water under standard conditions.

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Does the above graph show an exothermic or endothermic reaction?

Exothermic


The energy of the products is lower than the reactants, so energy has been lost to the surroundings.

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Does the above graph show an exothermic or endothermic reaction?

Endothermic


The energy of the products is higher than the reactants, so energy has been gained from the surroundings.

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What is an enthalpy profile diagram?

A diagram that shows the energy change during a chemical reaction.

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What is an endothermic reaction?

An endothermic reaction is a reaction that takes in energy from the surroundings, so the temperature of the surroundings decreases.

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What is an exothermic reaction?

An exothermic reaction is a reaction that transfers energy to the surroundings, so the temperature of the surroundings increases.

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