Question

Problem 4
Calculate the mass of ethane, C2H6, which must be burned to produce 100 kJ of heat.

2 CzH6(9) + 7 02(9) ---> 4CO2(g) + 6 H2O(1) AH = -3120 kJ​

Answer 1

Answer:

1.93 g

Explanation:

We are given;

The chemical equation;

2C₂H₆(g) + 7O₂(g) → 4CO₂(g) + 6H₂O(l) ΔH = -3120 kJ​

We are required to calculate the mass of ethane that would produce 100 kJ of heat.

• From the equation given;

• 2 moles of ethane burns to produce 3120 Kilo joules of heat

• Therefore;

Number of moles that will produce 100 kJ will be;

= (2 × 100 kJ) ÷ 3120 kJ)

= 0.0641 moles

• But, molar mass of ethane is 30.07 g/mol

Therefore;

Mass of ethane = 0.0641 moles × 30.07 g/mol

                          = 1.927 g

                          = 1.93 g

Thus, the mass of ethane that would produce 100 kJ of heat is 1.93 g

Answer 2

Taking into account the definition of enthalpy of a chemical reaction, the mass of C₂H₆ that must be burned to produce 100 kJ of heat is 1.927 g.

Enthalpy of a chemical reaction

The enthalpy of a chemical reaction as the heat absorbed or released in a chemical reaction when it occurs at constant pressure. That is, the heat of reaction is the energy that is released or absorbed when chemicals are transformed into a chemical reaction.

The enthalpy is an extensive property, that is, it depends on the amount of matter present.

Mass of C₂H₆ needed

In this case, the balanced reaction is:

2 C₂H₆ (g) + 7 O₂ (g) → 4 CO₂ (g) + 6 H₂O (l)

and the enthalpy reaction ∆H° has a value of -3120 kJ/mol.

This equation indicates that when 2 moles of C₂H₆ reacts with 7 moles of O₂ to produce 4 moles of CO₂ and 6 moles of H₂O, 3120 kJ of heat is released.

Then you can apply the following rule of three: If 3120 kJ are produced by 2 moles of C₂H₆, 100 kJ of heat are produced by how many moles of C₂H₆?

$amount of moles of C_{2} H_{6} =\frac{100 kJx2 moles}{3120 kJ}$

amount of moles of C₂H₆= 0.0641 moles

Being the molar mass of H₂O 30.07 g/mole, the mass of C₂H₆ that must be burned to produce 100 kJ of heat is:

0.0641 moles× 30.07 $\frac{g}{mole}$= 1.927 g

Finally, the mass of C₂H₆ that must be burned to produce 100 kJ of heat is 1.927 g.

Learn more about enthalpy of a chemical reaction:

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