Calculate the standard enthalpy change for the reaction
2A+B⇌2C+2D
Use the following data:
Substance ΔH∘f
(kJ/mol)
A -247
B -375
C 191
D -483
Express your answer to three significant figures and include the appropriate units.
My answer was 285 kJ/mol but mastering Chemistry says i was wrong
I agree with you.Book must be wrong.
To calculate the standard enthalpy change for a reaction using enthalpy of formation values, you can use the following equation:
ΔH° = Σ(nΔH°f(products)) - Σ(nΔH°f(reactants))
where ΔH° is the standard enthalpy change, n is the stoichiometric coefficient, and ΔH°f is the standard enthalpy of formation.
Let's calculate the standard enthalpy change for the given reaction:
Reactants:
2A + B
Σ(nΔH°f(reactants)) = 2(-247 kJ/mol) + (-375 kJ/mol)
Products:
2C + 2D
Σ(nΔH°f(products)) = 2(191 kJ/mol) + 2(-483 kJ/mol)
Putting the values into the equation, we get:
ΔH° = [2(191 kJ/mol) + 2(-483 kJ/mol)] - [2(-247 kJ/mol) + (-375 kJ/mol)]
ΔH° = 382 kJ/mol + (-966 kJ/mol) - 494 kJ/mol
ΔH° = -78 kJ/mol
Therefore, the standard enthalpy change for the reaction 2A + B ⇌ 2C + 2D is -78 kJ/mol.
To calculate the standard enthalpy change for a reaction, you need to use the equation:
ΔH° = (∑ΔH°f products) - (∑ΔH°f reactants)
Let's calculate the ΔH° for the given reaction:
2A + B ⇌ 2C + 2D
First, we need to determine the ΔH° for each reactant and product using the provided data:
ΔH°f for A = -247 kJ/mol
ΔH°f for B = -375 kJ/mol
ΔH°f for C = 191 kJ/mol
ΔH°f for D = -483 kJ/mol
Now, let's substitute these values into the equation:
ΔH° = [2(ΔH°f C) + 2(ΔH°f D)] - [2(ΔH°f A) + ΔH°f B]
ΔH° = [2(191 kJ/mol) + 2(-483 kJ/mol)] - [2(-247 kJ/mol) + (-375 kJ/mol)]
ΔH° = [382 kJ/mol - 966 kJ/mol] - [-494 kJ/mol - 375 kJ/mol]
ΔH° = -584 kJ/mol - (-869 kJ/mol)
ΔH° = -584 kJ/mol + 869 kJ/mol
ΔH° = 285 kJ/mol
Therefore, the standard enthalpy change for the reaction 2A + B ⇌ 2C + 2D is 285 kJ/mol.
It seems that your answer of 285 kJ/mol is correct. If your answer is not being accepted on Mastering Chemistry, double-check any rounding or units that may be required by the assignment.