Edexcel A-Level Chemistry 9CH0
Atomic Structure and the Periodic Table
Bonding and Structure
Inorganic Chemistry and the Periodic Table
Formulae, Equations and Amounts of Substance
Organic Chemistry I
Modern Analytical Techniques I
Energetics I
Kinetics I
Equilibrium I
Acid-Base Equilibria
Energetics II
Redox II
Transition Metals
Kinetics II
Organic Chemistry II
Organic Chemistry III
Energetics I
Enthalpy changes, standard definitions and calorimetry
- 3 things to know
- Papers 1 and 3
Overview
Enthalpy change and standard conditions, exothermic and endothermic signs and enthalpy level diagrams, the standard enthalpy changes of reaction, formation, combustion and neutralisation, using Q = mcΔT to find ΔH in kJ mol⁻¹, and the heat losses and assumptions that limit calorimetry.
What you need to know
Answer each one before you reveal it.
State the standard conditions used for enthalpy changes.
What is an enthalpy change?
Questions from this subtopic
Each one with the model answer underneath.
- 1
What is an enthalpy change?
Model answer
Heat taken in or given out while the pressure is held constant.
- 2
State the standard conditions used for enthalpy changes.
Model answer
A pressure of 100 kPa and a stated temperature, usually 298 K.
- 3
What is the sign of the enthalpy change for an exothermic reaction?
Model answer
Negative, because heat energy is released to the surroundings.
- 4
What is the sign of the enthalpy change for an endothermic reaction?
Model answer
Positive, because heat energy is taken in from the surroundings.
- 5
On an enthalpy level diagram, where are the products of an exothermic reaction relative to the reactants?
Model answer
Below the reactants, at lower enthalpy.
- 6
On an enthalpy level diagram, where are the products of an endothermic reaction relative to the reactants?
Model answer
Above the reactants, at higher enthalpy.
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