The solution of the problem involves the following steps:

Figure E$8\mathrm{.}5$

Calculate the combustion products via material balances.

Calculate the mole fraction of the water vapor in the combustion products as indicated just prior to this example.

Assume a total pressure, say, $1$atm, and calculate $y_{H_{2}O}{p}_{\text{t}\text{o}\text{t}\text{a}\text{l}}=p_{H_{2}O}$ in the combustion products. At equilibrium $p_{H_{2}O}$ will be the vapor pressure $p_{H_{2}O}^{**}.$

Condensation $($at constant total pressure$)$ would be possible when $p_{H_{2}O}^{**}$ equals the calculated $p_{H_{2}O}.$ This value is the dew point.

Look up the temperature corresponding to $p_{H_{2}O}$ in the saturated steam tables.