Determine the heat of combustion of acetylene (C2H2).

To determine the heat of combustion of acetylene (C2H2), you can use the principles of Hess's Law and the enthalpy of formation values for the reactants and products involved.

Hess's Law states that the overall enthalpy change of a reaction is independent of the pathway taken. This means that if we can break down the combustion of acetylene into a series of reactions with known enthalpy changes, we can calculate the overall heat of combustion.

The balanced equation for the combustion of acetylene is:
2C2H2(g) + 5O2(g) → 4CO2(g) + 2H2O(g)

To calculate the heat of combustion, we need to know the enthalpy of formation of each compound involved.

The enthalpy of formation (ΔHf) is the change in enthalpy when one mole of a compound is formed from its constituent elements in their standard states at a given temperature and pressure.

Using standard enthalpy of formation values, the equation becomes:
2ΔHf(C2H2) + 5ΔHf(O2) → 4ΔHf(CO2) + 2ΔHf(H2O)

By looking up the standard enthalpy of formation values in a reliable source or reference book, you can substitute them into the equation.

For example, the standard enthalpy of formation values for acetylene (C2H2), carbon dioxide (CO2), and water (H2O) are as follows:
ΔHf(C2H2) = 226.73 kJ/mol
ΔHf(CO2) = -393.51 kJ/mol
ΔHf(H2O) = -285.83 kJ/mol

The standard enthalpy of formation value for oxygen (O2) is zero since it exists naturally in its standard state.

Now, simply substitute the values into the equation and solve for the unknown enthalpy change:
2(226.73 kJ/mol) + 5(0 kJ/mol) → 4(-393.51 kJ/mol) + 2(-285.83 kJ/mol)

This calculation will give you the overall heat of combustion of acetylene.

Note: It is important to ensure all the units are consistent and in the correct format (e.g., kJ/mol) when performing calculations using enthalpy of formation values.