Energetics(needs finishing) Flashcards
What does the expression mol^-1 mean
Per mole
KJmol^-1 is the same at KJ/mol
What are the Standard conditions + symbol
100kPa
298K
ΔH ^ ⦵
What enthalpy is an exothermic reaction and why
Negative enthalpy change
Products end up with less heat energy than they started with as heat energy is lost to the surroundings
What enthalpy is endothermic reaction and why
Positive enthalpy change
Products end up with more energy as heat energy is taken in from the surroundings
Why is it important to have standard conditions
Pressure affects amount of heat energy given out by reactions that involve gases. More pressure requires more energy so less energy is released from the reaction
Enthalpy change of formation
Enthalpy change when 1 mole of a substance is formed from its constituent elements in the standard states while under standard conditions
Enthalpy change of combustion
Enthalpy change when 1 mole of a substance is completely burned in oxygen under standard conditions in their standard states
What is temperature related to in terms of particles
The average kinetic energy of these particles
What do you need to know to calculate the enthalpy change of a substance
Mass of substance that is being heated or cooled
Temp change
Specific heat capacity of substance
Equation for Enthalpy change
q = mc ΔT
where
q = enthalpy change Jmol^-1
m = mass (g)
c = specific heat capacity ( 4.18J/g/K)
T = Temp (K)
REMEMBER ENTHALPY CHANGE IS PER MOLE
What is Hess’s law?
The enthalpy change for a chemical reaction is the same, whatever route is taken from reactants to products
Hess law equation
ΔH1 = ΔH2 + ΔH3
