Explain the standard enthalpy of combustion $\left( \Delta_{c} H^{\theta} \right)$.

The standard enthalpy of combustion $\left( \Delta_{c} H^{\theta} \right)$ is defined as the enthalpy change per mole of a substance when it undergoes complete combustion,with all reactants and products being in their standard states at a specified temperature (usually $298 \ K$).
For example,cooking gas in cylinders contains mostly butane $(C_{4}H_{10})$. The thermo-chemical reaction is:
$C_{4}H_{10(g)} + \frac{13}{2} O_{2(g)}$ $\rightarrow 4 CO_{2(g)} + 5 H_{2}O_{(l)} ; \Delta_{c} H^{\theta} = -2658.0 \ kJ \ mol^{-1}$
Another example is the combustion of glucose:
$C_{6}H_{12}O_{6(s)} + 6 O_{2(g)}$ $\rightarrow 6 CO_{2(g)} + 6 H_{2}O_{(l)} ; \Delta_{c} H^{\theta} = -2802.0 \ kJ \ mol^{-1}$