Enthalpy Change Practical

Madeleine.Dc
Mind Map by Madeleine.Dc, updated more than 1 year ago
Madeleine.Dc
Created by Madeleine.Dc over 6 years ago
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Covers the calculations and methods for Enthalpy Change calculations
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Enthalpy Change Practical
1 Non-Combustion Reaction
1.1 Spontaneous reaction at room temperature
1.1.1 Salt + Water
1.1.1.1 Enthalpy change of solution
1.1.2 Acid + Alkali
1.1.2.1 Enthalpy change of neutralisation
1.2 Used for both exothermic and endothermic reactions
2 Combustion Reaction
2.1 Specifically measures the heat given out (exothermic)
2.2 Method
2.2.1 Measure the mass of the burner before and after
2.2.1.1 Thermometer records the temperature of the known mass of water
2.3 Limitations
2.3.1 Very Inaccurate
2.3.1.1 Huge losses of heat
2.3.1.1.1 Radiation from flame and calorimeter
2.3.1.1.2 Conduction through copper calorimeter
2.3.1.1.3 Convection from the flame gases passing by calorimeter
2.4 Used for the comparison of the heat output of different fuels
2.4.1 If same burner and set-up is used
3 Q = mcΔT
3.1 Calculation
3.1.1 For both experiements
3.1.1.1 Calculate the change in temperature
3.1.1.1.1 Apply mcΔT, using the heat capacity of and mass of water
3.1.1.1.1.1 Calculate the number of moles of reactants
3.1.1.1.1.1.1 Alcohol for combustion reaction, use mass = mr x mole
3.1.1.1.1.1.2 Q x 1/moles of burner
3.1.1.1.1.1.2.1 Put into KiloJoules
3.1.1.1.1.1.3 Solution, use moles = conc x vol
4 Free Energy
4.1 ΔG = ΔH - TΔS
4.1.1 ΔS(system) = S(products) - S(reactants)
4.1.1.1 Entropy
4.1.1.1.1 Measure of the disorder in a system
4.1.2 Use the temperature in Kelvin
4.1.2.1 273 + T in degress
4.1.3 Hess's law cycles can also be applied
4.2 If ΔG is positive the reaction is not spontaneous at 298K
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