Year one energetics 0.0 / 5 ? ChemistryEnergeticsA2/A-levelAQA Created by: champion1607Created on: 21-05-18 19:06 Define enthalpy change Heat is the hear energy transferred in a reaction at constant pressure 1 of 13 What is the symbol for enthalpy and the units? delta H and KJ mol-1 2 of 13 What are the standard conditions for enthalpy? 100KPa, 298K and all concentrations are 1 molar 3 of 13 Define exothermic Reactions that give out heat, ∆H is negative 4 of 13 Define endothermic Reactions that absorb energy, ∆H is positive 5 of 13 What type of reaction occurs when you break bonds? You need energy to break bonds, so bond breaking is endothermic 6 of 13 What type of reaction occurs when you form bonds? Energy is released when bonds are formed, so bond making is exothermic 7 of 13 Define bond enthalpy Energy required to break a certain amount of bonds, always will be ∆ 8 of 13 Why are book data values for enthalpy different from actual? Book values use mean bond enthalpies 9 of 13 State the calorimetry equation q = m x c x delta T, q= enthalpy change, m= mass of water g, c= 4.18, delta T= temp change in K 10 of 13 State Hess' law The total enthalpy change of a reaction is independent to the route taken 11 of 13 Define standard enthalpy of formation When 1 mole of a compound is formed from its elements in their standard states under standard conditions 12 of 13 Define standard enthalpy of combustion When 1 mole of a substance is completely burned in oxygen under standard conditions 13 of 13
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