Energetics Flashcards
(supplement with allery chemistry. for hess cycles use the two flashcards)
What is enthalpy change?
The heat energy change measured under conditions of constant pressure
What is enthalpy of formation?
Enthalpy change when one mole of a substance is produced from its elements with all substances in standard states, under standard conditions
What is enthalpy of combustion?
Enthalpy change when one mole of a substance is burned completely in oxygen with all substances in standard states, under standard conditions
What is the equation for enthalpy change?
q = mcΔT
m= mass, grams (of thing you are heating up)
c= specific heat capacity
T= change in temp, kelvin
What is specific heat capacity?
Energy required to raise 1g of substance by 1K without a change of state
How do you work out the enthalpy change per mole of a substance from the energy value (q)?
∆H=q/moles
What is Hess’s law?
Total enthalpy change of a reaction is independent of the route taken
How do you calculate the enthalpy of formation?
∆HfƟ = Σ∆H(products) - Σ∆H(reactants)
How do you calculate the enthalpy of combustion?
∆HcƟ = Σ∆H(reactants) - Σ∆H(products)
What is mean bond enthalpy?
Enthalpy needed to break one mole of the stated bond in a gaseous state, under standard conditions
How do you calculate mean bond enthalpy?
∆H = bonds broken (reactants) - bonds formed (products)
(+ve) (-ve)
