Energetics 0.0 / 5 ? ChemistryEnergeticsA2/A-levelAQA Created by: billywright666Created on: 11-01-18 21:19 Define standard enthalpy change. Heat (or energy) change under standard conditions. 1 of 15 What are standard conditions? Temp = 298K (25 degrees) Pressure = 100kPa (100000Pa use this value in PV=nRT) 2 of 15 Define Exothermic. (-)A release of energy giving a NEGATIVE enthalpy change (ΔH). 3 of 15 Define Endothermic. (+)A increase of energy from the surroundings giving a POSITIVE enthaly change(ΔH). 4 of 15 What is the unit for Enthalpy change(ΔH)? KJ/mol 5 of 15 What is the Average Bond Dissociation energy? The average energy it takes to break a particular bond. It is an average of the different states of the bonds ( solid, liquid and gas). 6 of 15 Define Calorimetry. The process of measuring the amount of heat realeased or absorbed during a chemical reactions (usually combusting fuels to find there energy release). 7 of 15 What is the equation for heat change in Joules? Q(J)= MCΔT (After using this to find ΔH you will need make it into KJ and divide by moles. J/mol) 8 of 15 Two reasons ΔH could be different to the data book value? 1. Heat loss to the surroundings 2. Incomplete combustion due to lack of oxygen. 9 of 15 Does the route taken affect the ΔH? No, in a reaction the ΔH for a reaction is the same for each route taken. 10 of 15 Define the Enthalpy of Formation. When one mole of a compound is formed form its constituent elements in their standard states, under standard conditions. 11 of 15 When finding the enthalpy of formation what do we ignore? Elements as they are already in their standard state. 12 of 15 Define the Enthalpy of Combustion. When one mole of a compound is burned completely in oxygen with all the reactants and products in there standard states under standard conditions. 13 of 15 In calculating ΔH of combustion what way do the arrows go? Downwards. 14 of 15 In calculating ΔH of formation what way do the arrows go? Upwards. 15 of 15
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