I need explanation for the below formula, as in, it's derivation and cause for inclusion of each symbol/part;
Q = S + I + 1/2 *D - E - U, where,
S is heat of sublimation
I is ionization energy
D is dissociation energy
E is electron affinity
U is lattice energy
Q is total heat change (with an example). What is total heat change, first of all?
Answers
Answer:
during any chemical reaction bonds r broken at reactant side and bonds r formed at product side, during this process energy either evolved or absorbed, energy required to complete the reaction is called total heat change.
Explanation:
Calculate the total heat change for the combustion of acetylene ( C2H2 )
Solution
2C2H2(g)+5O2(g)⟶4CO2(g)+2H2O(g)(3)
Given:
ΔHºf CO2 = -393.5 kJ/mole
Multiply this value by the stoichiometric coefficient, which in this case is equal to 4 mole.
vpΔHºf CO2 = 4 mol (-393.5 kJ/mole)
= -1574 kJ
ΔHºf H2O = -241.8 kJ/mole
The stoichiometric coefficient of this compound is equal to 2 mole. So,
vpΔHºf H2O = 2 mol ( -241.8 kJ/mole)
= -483.6 kJ
Now add these two values in order to get the sum of the products
Sum of products (Σ vpΔHºf(products)) = (-1574 kJ) + (-483.6 kJ) = -2057.6 kJ
given-
ΔHºf C2H2 = +227 kJ/mole
Multiply this value by the stoichiometric coefficient, which in this case is equal to 2 mole.
vpΔHºf C2H2 = 2 mol (+227 kJ/mole)
= +454 kJ
given-
ΔHºf O2 = 0.00 kJ/mole
The stoichiometric coefficient of this compound is equal to 5 mole. So,
vpΔHºf O2 = 5 mol ( 0.00 kJ/mole)
= 0.00 kJ
Add these two values in order to get the sum of the reactants
Sum of reactants (Δ vrΔHºf(reactants)) = (+454 kJ) + (0.00 kJ) = +454 kJ
The sum of the reactants and products can now be inserted into the formula:
ΔHº = Δ vpΔHºf(products) - ? vrΔHºf(reactants)
= -2057.6 kJ - +454 kJ
= -2511.6 kJ