Question

Calculate the enthalpy of combustion of ethylene gas to form CO₂ gas and H₂O gas at 298 K and 1 atmospheric pressure. The enthalpies of formation of CO₂, H₂O and C₂H₄ are –393.5, –241.8 + 52.3 kJ per mole respectively.

Answer 1

The enthalpy of combustion of ethylene gas to form CO2 gas and H2O gas is calculated by subtracting the sum of enthalpies of formation of reactants from that of the products, resulting in an enthalpy of combustion of -1218.3 kJ/mol.

Step-by-step explanation:

To calculate the enthalpy of combustion of ethylene gas (C2H4) to form CO2 gas and H2O gas at 298 K and 1 atmospheric pressure, you would use the given enthalpies of formation. The balanced chemical equation for the combustion of ethylene is:

C2H4(g) + 3O2(g) → 2CO2(g) + 2H2O(g)

To find the enthalpy of combustion, use the equation:

ΔHcomb = ∑ΔHf(products) - ∑ΔHf(reactants)

Plugging in the values:

ΔHcomb = [(2 × -393.5 kJ/mol) + (2 × -241.8 kJ/mol)] - [(1 × 52.3 kJ/mol) + (3 × 0 kJ/mol for O2)]

ΔHcomb = [(-787 kJ/mol) + (-483.6 kJ/mol)] - [52.3 kJ/mol]

ΔHcomb = -1270.6 kJ/mol + 52.3 kJ/mol

ΔHcomb = -1218.3 kJ/mol

Therefore, the enthalpy of combustion of ethylene is -1218.3 kJ/mol.

Answer 2

The enthalpy of combustion of ethylene gas (C2H4) at 298 K and 1 atmospheric pressure, calculated using the enthalpies of formation for the reactants and products, is -1323.3 kJ/mol.

Step-by-step explanation:

To calculate the enthalpy of combustion of ethylene gas (C2H4), we must consider the balanced chemical equation for its combustion:

• C2H4(g) + 3O2(g) → 2CO2(g) + 2H2O(g)

The enthalpy change for the reaction can be calculated using the enthalpies of formation of the reactants and products:

• ΔHcombustion = [∑ΔHf products] - [∑ΔHf reactants]

Using the given enthalpies of formation:

• CO2: -393.5 kJ/mol

• H2O: -241.8 kJ/mol

• C2H4: +52.3 kJ/mol

The enthalpy of combustion is:

• ΔHcombustion = [2(-393.5 kJ/mol) + 2(-241.8 kJ/mol)] - [+52.3 kJ/mol]

• ΔHcombustion = [(-787.0) + (-483.6)] - [52.3]

• ΔHcombustion = -1323.3 kJ/mol

Therefore, the enthalpy of combustion of ethylene gas at 298 K and 1 atmospheric pressure is -1323.3 kJ/mol.