Calculating enthalpy changes Flashcards
What is the equation for enthalpy change of reaction?
ΔrxnH = ΣvΔfH (products) - ΣΔfH (reactants)
What is the enthalpy of fusion for water?
H2O (s) -> H2O (l)
What is the enthalpy of vaporisation for water?
H2O (l) -> H2O (g)
What is the equation for electrical heating?
q = itV
What is the equation linking sublimation, vaporization, fusion
ΔSubH = ΔFusH + ΔvapH
What would you need to calculate ΔSubH at 0 degrees?
ΔfusH and ΔvapH at zero degrees
What is an example of an ionisation equation?
H(g) -> H+ (g) + e-
What is an example of an electron gain equation?
Cl (g) + e- -> Cl- (g)
What is an example of a bond dissociation equation?
HCl (g) -> H (g) + Cl (g)
How would you work out the heat required for the ionisation of a specific amount of metal?
Use the ionisation energies and work out the number of moles from the grams
Use the equation q = n x ΔH
What are mean bond enthalpies?
Bond enthalpies are averages for related compounds
What is the enthalpy of combustion?
Enthalpy change when 1 mole of a substance is combusted to liquid water and gaseous CO2 and N2 under standard conditions
How do you work out the specific enthalpy for combustion?
Specific enthalpy = ( ΔcomH / kJ mol⁻¹ ) / ( Molar mass / gmol⁻¹)
What is an example equation for dissolution of a salt?
NaCl (s) -> Na+(aq) + Cl-(aq)
What is an example equation of lattice enthalpy for dissolution of a salt?
NaCl (s) -> Na+(g) + Cl-(g)
What is an example equation of solvation energy for dissolution of a salt?
Na+(g) -> Na+(aq)
Cl-(g) -> Cl-(aq)
What is lattice energy mainly?
Electrostatic
What is coulomb’s law?
The magnitude of the electrostatic force of attraction or repulsion between two point charges is directly proportional to the product of the magnitudes of changes and inversely proportional to the square of the distance between them
What is the equation for coulomb’s law?
l F l = Q1 Q2 / 4πεr²
What is the equation for the permitivity?
ε = εoεr
