Question detail
What is the enthalpy change when 2 moles of water are formed from hydrogen and oxygen gases? Given that the enthalpy of formation of water is -286 kJ/mol, calculate the total enthalpy change for this reaction.
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Question
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Topic
A-level practical endorsement and required practical activities
Question
What is the enthalpy change when 2 moles of water are formed from hydrogen and oxygen gases? Given that the enthalpy of formation of water is -286 kJ/mol, calculate the total enthalpy change for this reaction.
Answer
The total enthalpy change for the formation of 2 moles of water is -572 kJ. This answer is anchored to A-level required practical activities.
Explanation
The total enthalpy change for the formation of 2 moles of water is -572 kJ. is the best answer because it directly supports the AQA A-Level Chemistry objective to required practical 2: measure an enthalpy change. This reasoning is anchored to A-level required practical activities in A-level practical endorsement and required practical activities, and it separates enthalpy from similar A-Level ideas rather than relying on a vague recall statement. Other options are weaker if they use the wrong evidence, calculation, mechanism, observation, unit, or conclusion for this subtopic.
Common mistake
Misunderstanding Enthalpy Change Measurement
Students often confuse the enthalpy change with the total heat released or absorbed during a reaction, neglecting to consider the specific heat capacity of the solution used.
To correctly measure the enthalpy change, use the formula q = mcΔT, where q is the heat energy, m is the mass of the solution, c is the specific heat capacity, and ΔT is the change in temperature. For example, if 100 g of water (c = 4.18 J/g°C) is heated from 20°C to 25°C, substitute into the formula: q = 100 g × 4.18 J/g°C × (25°C - 20°C) = 2090 J. Therefore, the enthalpy change is 2090 J. Keep the correction anchored to A-level required practical activities and the objective: Required practical 2: measure an enthalpy change.
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