Key Principles Flashcards
What is the energy of a substance called?
- Enthalpy (H)
Can Enthalpy be measured?
- NO
- However enthalpy change (ΔH) is easy to measure
In a reaction (at constant pressure) the amount of heat energy absorbed or produced is equal to what?
- The change in enthalpy
What is a state function?
- A property whose value does not depend on the path taken to reach that specific value
What is internal energy?
- Internal energy is the sum of all microscopic energies
E.g. - Kinetic energy from:
— molecular translations
— rotations
— vibrations
— potential energy from inter and intra-molecular interactions
What is Work?
Movement against resistance (not heat)
E.g. Lifting against gravity
Define enthalpy change of formation (ΔfH).
Enthalpy change when 1 mole of a compound is formed from its constituent elements in their standard states under standard conditions
What are the standard conditions?
298K
1.00 x 10^5 PA
What is the (ΔfH°) of an element in its standard form?
- Always 0 kJ mol^-1
- E.g. O2
What does each symbol in the standard enthalpy change, (∆rH°(T)) equation mean?
– ∆ = change
– r = for the reaction (lots of other types we’ll see later)
– H = enthalpy
– ° = standard state conditions at 1 bar (1.00 x105 Pa)
– T = at a given temperature, eg 298.15K
– as state can change
– Physical states given (s, l, g)
– for one mole of pure substance
What units are enthalpy change given in?
- kJ mol^-1
Symbol for enthalpy of formation?
ΔHf°
Symbol for enthalpy of combustion?
ΔHc°
Symbol for enthalpy of neutralisation?
ΔHN°
Symbol for enthalpy of vaporisation?
ΔHvap°
