Question

From the following reaction, calculate the amount of heat liberated during formation of 75 g ethane. (At mass: C = 12, H = 1)

$C_2H_4(g) + H_2(g) \rightarrow C_2H_6(g); \Delta H = -124 \, \text{kJ mol}^{-1}$

• A. 248 kJ
• B. 310kJ
• C. 372 kJ
• D. 284 kJ

Answer 1

Answer: (B)

310 kJ

Answer 2

1. Calculate moles of ethane ($C_2H_6$):

   Molar mass of $C_2H_6 = 2 \times 12 + 6 \times 1 = 30 \, \text{g/mol}$

   Moles $= \frac{75 \, \text{g}}{30 \, \text{g/mol}} = 2.5 \, \text{mol}$

2. Determine total heat liberated:

   Given $\Delta H = -124 \, \text{kJ}$ per mole of ethane formed.

   Total heat $= 2.5 \, \text{mol} \times (-124 \, \text{kJ/mol}) = -310 \, \text{kJ}$

   Heat liberated is $310 \, \text{kJ}$.