Question

Using the equations and enthalpy values provided, which mathematical expression can be used to determine the unknown enthalpy change represented by x?
3C + 3O2 yields 3CO2 deltaH = -1182 kJ

4H2 + 2O2 yields 4H2O deltaH =-1144 kJ

C3H8 + 5O2 yields 3CO2 + 4H2O deltaH = x

3H8 3C + 4H2 H = 104 kJ

A. 104 = (-1182) - [x + (-1144)]

B.104 = x - [(-1182) + (-1144)]

C.104 = (-1182) + (-1144) + x

D.104 = x + (-1182) - (-1144)

Answer 1

Answer:

B. 104 = x - [(-1182) + (-1144)]

Explanation:

The unknown entahlpy change for the given equation is determined by the Hess's Law.

3C + 3O2 → 3CO2  ΔH = -1182 kJ      ....(a)

4H2 + 2O2  → 4H2O  ΔH =-1144 kJ   ....(b)

C3H8 → 3C + 4H2  ΔH  = 104 kJ  ....(c)

C3H8 + 5O2  →  3CO2 + 4H2O   ΔH = x   ....(d)

The unknown enthalpy change x is calculated as follows,

The equation (d) is obtained by the adding equation (a), equation (b ) and equation (c) .Therefore, the value of the unknown enthalpy change x will be equal to the sum of all enthalpy change value of the respective equation.

104 = x - [(-1182) + (-1144)]

Answer 2

In order to solve this, we need to make use of Hess' Law.

We are already given the equations and their corresponding deltaH. Using Hess' Law, we can generate this equation:
104 kJ = x - (-1182 kJ) - (-1144 kJ)

Among the choices, the answer is
B.104 = x - [(-1182) + (-1144)]