Enthalpy changes Flashcards
What is enthalphy?
Internal energy + Pressure x Vol
How are reactions that:
Give out energy
Take in energy
named?
Give out = Exothermic = -ΔH
Take in = Endothermic = +ΔH
What does ΔH mean and what does it mean when it is positive?
ΔH means a change in enthalpy
What is the system in terms of enthalpy?
The reactants and the products
What are the surroundings in a reaction?
The rest of the universe
What is activation energy?
The minimum energy required for a reaction to start
What is the equation for energy change?
q = mass x Specific heat capacity x ΔT
g J per gram per Kelvin Degrees C
How is ΔH calculated from change in energy (q)?
- q
ΔH = ———–
moles
How do we measure enthalpy changes?
Record the change in temperature and mass of the substance and use that in a calculation.
What is the standard enthalpy change of formation, ΔfH?
The enthalpy change that takes place when 1 mole of compound is formed from its elements under standard conditions, with all reactants and products in their standard states.
What is the standard enthalpy change of neutralisation, ΔneutH?
The enthalpy change that accompanies the reaction of an acid and a base to form one mole of H2O(l) under standard conditions, with all reactants and products in their standard states.
What is the standard enthalpy change of combustion, ΔcH?
The enthalpy change that takes place when 1 mole of substance reacts completely with oxygen under standard conditions, with all reactants and products in their standard states.
What is Hess’s Law?
If a reaction can take place by more than one route and the initial and final conditions are the same, the total enthalpy change is the same for each route.
What is 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.
What is the order of the practical to measure the enthalpy change of combustion?
Spirit burner is weighed
Spirit burner is burned under a flask of water with a thermometer
Change in temperature of water is measured
Change in mass of the spirit burner is measured
