BRAINCAKEEnthalpy
Revision notes for Enthalpy in OCR Chemistry A (H032). Read the start of any lesson here, then sign in free for the whole lesson, the R.E.C.I.P.E. recall steps and the quiz.
- Enthalpy and Enthalpy ChangesEnthalpy is a measure of the total energy of a chemical system.
- Endothermic and Exothermic ReactionsThe law of conservation of energy states that energy cannot be created or destroyed.
- Activation EnergyFor a chemical reaction to occur, the bonds within the reactants must be broken and new bonds must be formed between the atoms to make the products.
- Standard Enthalpy Changes and Standard ConditionsEnthalpy changes are measured on a set of standard conditions as the enthalpy changes can vary with temperature, pressure or concentration.
- Enthalpy Change of ReactionThe standard enthalpy change of reaction ΔrHθ is the enthalpy change that accompanies a reaction in the molar quantities shown in a chemical…
- Enthalpy Change of FormationThe standard enthalpy change of formation ΔfHθ is the enthalpy change that takes place when one mole of a compound is formed from its elements under…
- Enthalpy Change of CombustionThe standard enthalpy change of combustion ΔcHθ is the enthalpy change that takes place when one mole of a substance reacts completely with oxygen…
- Enthalpy Change of NeutralisationThe standard enthalpy change of neutralisation ΔneutHθ is the energy change that accompanies the reaction of an acid with a base to form one mole of…
- Measuring the Enthalpy Change of CombustionA known volume e.g.
- Accuracy of Experimental ValueThe data book value for methanol is -726 kJmol-1.
- Determining the Enthalpy Change of a ReactionWhen carrying out the enthalpy change of a reaction between two aqueous solutions, the immediate surrounding is the solution itself, so a…
- Cooling CurvesCooling curves correct for heat loss to the surroundings.
- Average Bond EnthalpyThe average bond enthalpy is the energy required to break one mole of a specified type of bond in a gaseous molecule.
- Calculating Enthalpy Changes from Bond Enthalpiesbond mean bond enthalpy kJmol-1 N≡N 945 H-H 436 N-H 391 N2(g) + 3H2(g) → 2NH3(g) The enthalpy change is calculated from total bond enthalpies…
- Limitations of Bond Enthalpy CalculationsThe actual energy involved in breaking and forming the individual bonds will be different from the average bond enthalpies given in the data book…
- Hess's LawIf a reaction can take place by two routes the total enthalpy change for each route is the same provided that the starting and finishing conditions…
- Determination of Enthalpy Change of a Reaction from Enthalpies of Formation Using Hess's LawThe standard enthalpy change of any reaction can be obtained from the standard enthalpies of formation ΔHf of the reactants and products.
- Determination of Enthalpy Change of a Reaction from Enthalpies of Combustion using Hess's LawFor the formation of butane from its elements in their standard states, 4C(s) + 5H2(g) → C4H10(g) The enthalpy of formation of butane would be…
- Exam-style QuestionMethane reacts with steam to produce carbon monoxide and hydrogen.