Question

Hydrogenation reactions, in which H2 and an "unsaturated" organic compound combine, are used in the food, fuel, and polymer industries. In the simplest case, ethene (C2H4) and H2 form ethane (C2H6). If 140 kJ is given off per mole of C2H4 reacting, How much heat (in MJ) is released when 12 kg of C2H6 forms?

Answer 1

Answer: The amount of heat released is 56 MJ.

Explanation:

To calculate the number of moles, we use the equation:

$\text{Number of moles}=\frac{\text{Given mass}}{\text{Molar mass}}$  

Given mass of $C_2H_6$ = 12 kg = 12000 g    (Conversion factor: 1 kg = 1000 g)

Molar mass of $C_2H_6$ = 30 g/mol

Putting values in above equation, we get:

$\text{Moles of }C_2H_6=\frac{12000g}{30g/mol}=400mol$

The chemical reaction for hydrogenation of ethene follows the equation:

$C_2H_4+H_2\rightarrow C_2H_6$

By Stoichiometry of the reaction:

When 1 mole of ethane releases 140 kJ of heat.

So, 400 moles of ethane will release = $\frac{140}{1}\times 400=56000kJ$ of heat.

Converting this into Mega joules, using the conversion factor:

1 MJ = 1000 kJ

So, $\Rightarrow 56000kJ\times (\frac{1MJ}{1000kJ})=56MJ$

Hence, the amount of heat released is 56 MJ.

Answer 2

A type of chemical reaction in which the element or the compound react with molecular hydrogen is called a hydrogenation reaction.

56 MJ is the amount of heat released.

What is heat in a hydrogenation reaction?

Given,

Mass of $\rm C_{2}H_{6}$ = 12000g

molar mass  $\rm C_{2}H_{6}$ = 30 g/mol

Calculate the number of moles of $\rm C_{2}H_{6}$ :

$\begin{aligned}\rm Moles &= \dfrac{\rm Mass}{\rm Molar\; mass} \\\\&= \dfrac{12000}{30}\\\\&= 400 \;\rm mol \end{aligned}$

The chemical reaction of the hydrogenation can be given as:

$\rm C_{2}H_{4} + H_{2} \rightarrow C_{2}H_{6}$

From the above reaction, the stoichiometry coefficient gives,

1 mole of ethane = 140 kJ of heat

400 moles =  X heat

Solving for X:

$\begin{aligned}\rm X &= \dfrac{140}{1}\times 400\\\\&= 56000 \;\rm kJ\end{aligned}$

Convert the kJ into the MJ as:

1 MJ = 1000 kJ

X MJ = 56000 kJ

Solving for X:

$\begin{aligned} \rm X &= 56000\;\rm kJ \times (\dfrac {1\;\rm MJ}{1000\;\rm kJ})\\\\&= 56\;\rm MJ\end{aligned}$

Therefore, 56 MJ is the amount of heat released.

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