11/2/22 - Enthalpy and Hess' Law Flashcards
What is the relationship between the amount of heat gained by a system and the amount of heat lost by the surroundings?
q lost = -q gained
q systems = -q surroundings
In constant volume calorimetry, how do you find the heat (q) lost or gained?
q of calorimeter = (C of calorimeter) x (ΔT of calorimeter)
C = heat capacity
What is Hess’ Law?
The total enthalpy change of a process is equal to the sum of the enthalpy changes of individual steps.
What is standard enthalpy of formation (ΔHºf)?
The change in enthalpy when 1 mole of a substance is formed from its elements in their standard states at constant pressure.
What is a substance’s standard state?
Its most stable form under standard conditions. Think of it like elemental form.
What are standard conditions?
1 atm of pressure at a given temperature, usually 25ºC.
What is the standard enthalpy of formation (ΔHºf) for O2?
0, as with all elements in their standard state.
What is the standard enthalpy of formation (ΔHºf) for Ca?
0, as with all elements in their standard state.
What is a standard formation reaction?
One 1 mole of a product is formed from reactants in their standard states.
