What is a:
System = Chemicals in a reaction
Surroundings = Everything else (universe)
What would the energy diagram of a exothermic reaction look like? Why?
What would the energy diagram of a endothermic reaction look like? Why?
Sign and effect on tempertature:
Exothermic = ΔH = -ve and increase in temperature
Endothermic = ΔH = +ve and decrease in temperature
Equations for finding the enthalpy of a reaction
q = mcΔT
ΔH = q/number of moles
SI units for q, m, c and ΔT when using q = mcΔT
q = J
m = 1g = 1cm3
c = Jg-1K-1
ΔT = K or ºC
3 reasons why water is most frequently used as the heat sink?
1. Very high specific heat capacity (sensitive experiment). Reaction will be more accurate.
2. Don't need to weight it. 1g = 1cm3
3. Assume that all heat energy will be given to water as the chemical reaction will take place in water, the chemicals are water soluble.
Specific heat capacity of water?
Define Hess's law
If you can go from reactants to products by 2 different routes. The enthalpy change of each route must be the same. the initial andfinal conditions are the same.
What is the average bond enthalpy?
The average enthalpy change that takes place when breaking by homolytic fission 1 mole of a given type of bond in the molecules of a gaseous species
Signs for breaking and making bonds. Which is exothermic/endothermic
Breaking bonds = Always positive (endothermic)
Making new bonds = Always negative (exothermic)
Formular for percentage error
[ (Apparatus error x Number of uses) / Value measured ] x 100