Question

The heat combustion of acetylene, C2H2(g), at 25°C, is –1299 kJ/mol. At this temperature, ΔHvalues for CO2(g) and H2O(l) are –393 and –286 kJ/mol, respectively. Calculate ΔHfor acetylene.

Answer 1

The enthalpy change for the combustion of acetylene can be calculated using Hess's Law. By subtracting the enthalpy changes for the formation of CO2(g) and H2O(l) from the enthalpy change for the combustion of acetylene, we can find the enthalpy change for the reaction. The enthalpy change for the combustion of acetylene is -1068 kJ/mol.

Step-by-step explanation:

The heat of combustion for acetylene, C2H2(g), can be calculated using Hess's Law, which states that the enthalpy change for a reaction is independent of the pathway taken. We can use the enthalpy values given for CO2(g) and H2O(l) to find the enthalpy change for the combustion of acetylene by subtracting the enthalpy changes for the formation of these compounds from the enthalpy change for the combustion of acetylene.

The balanced equation for the combustion of acetylene is:

C2H2(g) + 5/2O2(g) → 2CO2(g) + H2O(l)

From the given information, the enthalpy changes for the formation of CO2(g) and H2O(l) are -393 kJ/mol and -286 kJ/mol, respectively.

Using Hess's Law, we can calculate the enthalpy change for the combustion of acetylene as:

ΔHcombustion = 2(-393 kJ/mol) + (-286 kJ/mol)

ΔHcombustion = -782 kJ/mol + (-286 kJ/mol)

ΔHcombustion = -1068 kJ/mol

Answer 2

Using the information in the table to the right, calculate the enthalpy of combustion of each of the following substances: acetylene: ⇒ -1,256 kJ/mol ethanol: ⇒ -1,277 kJ/mol This is from a different problem on Edgenuit.y but hope this helps someone who couldn’t find the answer like me.