Chemistry, asked by presto, 11 months ago

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

Answered by jesuscallprashant
1

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

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