Energy changes for Edexcel A-level Chemistry
This page covers the following topics:
1. Thermal energy
2. Enthalpy change
3. Reaction profile
Calorimetry measures enthalpy changes from combustion using the equipment shown. It can also be used to measure other reactions using a beaker with a cork stopper and thermometer.
Enthalpy is the overall energy content of substances in a reaction, it is represented by ∆H. In order to compare reactions and calculate energy changes accurately ∆H is calculated using theoretical standard conditions.
Energy change of reaction may need to be calculated to determine whether a reaction is exothermic or endothermic and sketch the reaction profile.
What are the standard conditions?
substances in their standard states, at 298 K (25°C, roughly room temperature), at a pressure of 100 kPa (1 atm) with a 1 mol/L concentration
Is activation energy higher in endothermic or exothermic reactions?
Given that ΔH for the breakdown of ammonia is +92.9 kJ/mol, which reaction profile best fits this reaction? Why?
Graph 2, in which case the products have more energy than the reactants and ΔH is indicated by an upwards arrow.
The ΔHOC of methane is -882KJ/mol, what does this mean?
882KJ of energy is released when methane reacts completely with oxygen under standard conditions.
Sketch an endothermic reaction profile and indicate ΔH.
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