3.2.1 Enthalpy Changes Flashcards
Define Enthalpy change
Heat energy change
what are standard conditions?
298K at 100kPa
Define activation energy
The minimum energy required for a reaction to take place
Draw an enthalpy profile diagram for endothermic and exothermic reactions
Answers in link below
https://docs.google.com/document/d/17_ChjSZF0Sc_dkYUKqLJrHYHaeOCpJga1vV2fxhPb5M/edit?usp=sharing
What happens to energy in a endothermic reaction?
More energy is needed to break bonds than make them so energy is taken in from the surroundings, this makes the ΔH positive
What happens to energy in an exothermic reaction?
More energy is needed to make bonds meaning that energy is released into the surroundings causing ΔH to be negative
Define Enthalpy change of reaction
The enthalpy change associated with specified reaction. When substances react completely under standard states and conditions
Define Enthalpy change of Formation
The enthalpy change when one mole of substance is produced from its reactants under standard states and conditions
Define Enthalpy change of combustion
The enthalpy change when 1 mole of a substance is burned completely with oxygen under standard conditions
Define Enthalpy change of Neutralisation
The enthalpy change when solutions of acid and alkali react together to produce 1 mol of water under standard conditions
What is the calorimetry equation?
ΔH = (-mcΔt) / 1000n
m=mass (can be cm3 or grams, g takes priority, it must be what is being heated)
c= 4.18
Δt = temp change Celsius
n=moles
why may values found using calorimetry not be accurate?
Energy is easily lost by the system, so may be lost due to conduction, convection
inaccuracies can be reduced by putting on a lid or using an insulator like a polystyrene cup
Also the specific heat capacity of water is used which may not be accurate to solution being used
heat capacity of apparatus
incomplete combustion
evaporation of things
How do you find the enthalpy change with bond enthalpies?
enthalpyΔ = (ΔH of all bonds breaking) - ( ΔH of all bonds being made)
bonds breaking for all reactants
bonds being made: if a c=c bond is broken, then a c-c bond is made
What is Hess’s Law?
The overall enthalpy for a reaction will be the same regardless of the route taken
if you have enthalpy of FORMATION VALUESdo arrows go up of down?
UP
