Topic 8 - Energetics 1 Flashcards
Define standard enthalpy change of formation
The enthalpy change when one mole of a compound is formed in its standard state from its elements in their standard states.
Define standard enthalpy change of combustion
The enthalpy change when one mole of a substance undergoes complete combustion under standard conditions. All reactants and products are in their standard states.
What are standard conditions?
Atmospheric pressure of 1 atm (100 kPa)
A specified temperature usually, but not necessarily, 298 K (25ºC).
A concentration of 1 mol dm-3 for reactions with aqueous solutions.
What is Hess’s Law
The change in enthalpy of a reaction is the same whether the reaction takes place in one step of a series of steps.
What is enthalpy change?
The change in heat energy at a constant pressure
Define standard enthalpy change of a reaction
The enthalpy change that accompanies a reaction in the molar quantities expressed in a chemical equation under standard conditions, all reactants and products being in their standard states.
Define standard enthalpy of neutralisation
The enthalpy change when acid reacts with base to form one mole of water under standard conditions. All reactants and products are in their standard states.
What is the equation to calculate energy transferred, q, from a calorimetry experiment?
q = mcΔT
q = energy transferred (J)
m = mass of water (g)
c = specific heat capacity (J g-1 K-1)
ΔT = change in temperature (initial - final)
When making a Hess cycle with formation data:
What direction are the arrows?
What goes in the box underneath?
Up arrows
Elements
When making a Hess cycle with combustion data:
What direction are the arrows?
What goes in the box underneath?
Down arrows
Combustion products
