Question

did i get this
how much heat is produced by burning 19.5 g of acetylene (c₂h₂) under standard state conditions?

kj

how many moles of isooctane (c₈h₁₈) must be burned to produce 1120 kj of heat under standard
state conditions?

mol

Explanation:

Step1: Calculate moles of acetylene

The molar mass of \(C_2H_2\) is \(M=(2\times12 + 2\times1)\space g/mol=26\space g/mol\).
The number of moles \(n=\frac{m}{M}\), where \(m = 19.5\space g\). So \(n=\frac{19.5\space g}{26\space g/mol}=0.75\space mol\).
The standard enthalpy of combustion of \(C_2H_2\) is \(\Delta H=-1299.5\space kJ/mol\).
The heat produced \(q=n\times|\Delta H|\), so \(q = 0.75\space mol\times1299.5\space kJ/mol = 974.625\space kJ\)

Step2: Calculate moles of isooctane

The standard enthalpy of combustion of \(C_8H_{18}\) is \(\Delta H=-5461\space kJ/mol\).
We know that \(q=n\times|\Delta H|\), and we want \(q = 1120\space kJ\).
So \(n=\frac{q}{|\Delta H|}=\frac{1120\space kJ}{5461\space kJ/mol}\approx0.205\space mol\)

Answer:

974.625 kJ
0.205 mol