propyne, propylene, and propane

[logistic_guy]

The standard enthalpies of formation of gaseous propyne $\displaystyle (C_3H_4)$, propylene $\displaystyle (C_3H_6)$, and propane $\displaystyle (C_3H_8)$ are $\displaystyle +185.4, +20.4,$ and $\displaystyle -103.8$ kJ/mol, respectively. $\displaystyle \left(\bold{a}\right)$ Calculate the heat evolved per mole on combustion of each substance to yield $\displaystyle CO_2(g)$ and $\displaystyle H_2O(g)$. $\displaystyle \left(\bold{b}\right)$ Calculate the heat evolved on combustion of $\displaystyle 1$ kg of each substance. $\displaystyle \left(\bold{c}\right)$ Which is the most efficient fuel in terms of heat evolved per unit mass?

 

[khansaheb]

The standard enthalpies of formation of gaseous propyne $\displaystyle (C_3H_4)$, propylene $\displaystyle (C_3H_6)$, and propane $\displaystyle (C_3H_8)$ are $\displaystyle +185.4, +20.4,$ and $\displaystyle -103.8$ kJ/mol, respectively. $\displaystyle \left(\bold{a}\right)$ Calculate the heat evolved per mole on combustion of each substance to yield $\displaystyle CO_2(g)$ and $\displaystyle H_2O(g)$. $\displaystyle \left(\bold{b}\right)$ Calculate the heat evolved on combustion of $\displaystyle 1$ kg of each substance. $\displaystyle \left(\bold{c}\right)$ Which is the most efficient fuel in terms of heat evolved per unit mass?

show us your effort/s to solve this problem.

 

[logistic_guy]

show us your effort/s to solve this problem.

Let me try to solve (a) for propyne. The combustion reaction is:

$\displaystyle \text{C}_3\text{H}_4(g) + 4\text{O}_2(g) \rightarrow 3\text{CO}_2(g) + 2\text{H}_2\text{O}(g)$

The heat per mole is:

$\displaystyle \Delta H = \sum n\Delta H^{\circ}_f(\text{products}) - \sum m\Delta H^{\circ}_f(\text{reactants})$

where $\displaystyle \Delta H^{\circ}_f$ is the standard enthalpy of formation.

$\displaystyle \Delta H = [3\Delta H^{\circ}_f(\text{CO}_2) + 2\Delta H^{\circ}_f(\text{H}_2\text{O})] - [\Delta H^{\circ}_f(\text{C}_3\text{H}_4) + 4\Delta H^{\circ}_f(\text{O}_2)]$

The standard enthalpy of formation for propyne was given, but for carbon dioxide and water, I have to look at the table.


The standrard enthalpy of formation of any element in its most stable form such as $\displaystyle \text{O}_2$ is defined to be zero.

$\displaystyle \Delta H = [3(-393.5) + 2(-241.8)] - [(185.4) + 4(0)] = -1849.5 \ \text{kJ/mol}$

I will continue in the next post.

 

[logistic_guy]

Let us start with the combustion reaction for propylene.

$\displaystyle \text{C}_{3}\text{H}_{6}(g) + 4.5\text{O}_{2}(g) \rightarrow 3\text{C}\text{O}_{2}(g) + 3\text{H}_{2}\text{O}(g)$

 

[logistic_guy]

$\displaystyle \bold{(b)} \rightarrow \ \text{propylene}$

$\displaystyle \Delta H = [3\Delta H^{\circ}_f(\text{CO}_2) + 3\Delta H^{\circ}_f(\text{H}_2\text{O})] - [\Delta H^{\circ}_f(\text{C}_3\text{H}_6) + 4.5\Delta H^{\circ}_f(\text{O}_2)]$

$\displaystyle = [3(-393.5) + 3(-241.8)] - [(20.4) + 4.5(0)] = -1926.3 \ \text{kJ/mol}$