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290449
Enthalpy Change Practical
Description
Covers the calculations and methods for Enthalpy Change calculations
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a2
as
chemistry
energy
chemistry
energy
gce
Mind Map by
Madeleine.Dc
, updated more than 1 year ago
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Created by
Madeleine.Dc
almost 11 years ago
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Resource summary
Enthalpy Change Practical
Non-Combustion Reaction
Spontaneous reaction at room temperature
Salt + Water
Enthalpy change of solution
Acid + Alkali
Enthalpy change of neutralisation
Used for both exothermic and endothermic reactions
Combustion Reaction
Specifically measures the heat given out (exothermic)
Method
Measure the mass of the burner before and after
Thermometer records the temperature of the known mass of water
Limitations
Very Inaccurate
Huge losses of heat
Radiation from flame and calorimeter
Conduction through copper calorimeter
Convection from the flame gases passing by calorimeter
Used for the comparison of the heat output of different fuels
If same burner and set-up is used
Q = mcΔT
Calculation
For both experiements
Calculate the change in temperature
Apply mcΔT, using the heat capacity of and mass of water
Calculate the number of moles of reactants
Alcohol for combustion reaction, use mass = mr x mole
Q x 1/moles of burner
Put into KiloJoules
Solution, use moles = conc x vol
Free Energy
ΔG = ΔH - TΔS
ΔS(system) = S(products) - S(reactants)
Entropy
Measure of the disorder in a system
Use the temperature in Kelvin
273 + T in degress
Hess's law cycles can also be applied
If ΔG is positive the reaction is not spontaneous at 298K
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