Question

1. In the presence of some metals, ethylene (C2H4) and hydrogen gas react to form ethane (C2H6) according to the following thermochemical equation:
C2H4(g) + H2(g)---> C2H6(g) triangle H°= -136.98 kJ
If the molar mass of ethylene is 28.05 g/mol, how much heat is liberated when 100.0 g of ethylene reacts?


2. How much it was prior to convert 20.0 g of ice at -50.0°C to liquid water at 0.0°C?
The specific heat of ice is 2.06 J/(g•°C) and the heat of fusion of water is 334 J/g.


3. Under certain conditions, nitrogen gas and oxygen gas react to form the toxic brown gas nitrogen dioxide: N2(g) + 2 O2(g) ---> 2 NO2(g). For this reaction, triangle H°= 66.2 kJ and triangle S°= -121.81 J/K; calculate triangle G° at standard conditions (298 K and 1 atm) and determined if a reaction is spontaneous, nonspontaneous, or an equilibrium at these conditions.

Answer 1

Answer on question #70171 – Chemistry – General Chemistry

1. In the presence of some metals, ethylene (C2H4) and hydrogen gas react to form ethane (C2H6) according to the following thermochemical equation:

$$\mathrm{C2H4(g)} + \mathrm{H2(g)} \longrightarrow \mathrm{C2H6(g)} \text{ triangle } \mathrm{H}^{\circ} = -136.98\ \mathrm{kJ}$$

If the molar mass of ethylene is $28.05\ \mathrm{g/mol}$, how much heat is liberated when $100.0\ \mathrm{g}$ of ethylene reacts?

**Solution:**

$$\begin{array}{l} 28.05\ \mathrm{g} - -136.98\ \mathrm{kJ} \\ 100\ \mathrm{g} - x\ \mathrm{kJ} \\ x = \frac{-136.98 \cdot 100}{28.05} = -495.47\ \mathrm{kJ}. \end{array}$$

**Answer:** $-495.47\ \mathrm{kJ}$.

2. How much it was prior to convert $20.0\ \mathrm{g}$ of ice at $-50.0^{\circ}\mathrm{C}$ to liquid water at $0.0^{\circ}\mathrm{C}$? The specific heat of ice is $2.06\ \mathrm{J/(g\cdot^{\circ}C)}$ and the heat of fusion of water is $334\ \mathrm{J/g}$.

**Solution:**

$$\begin{array}{l} Q = Q_1 + Q_2 \\ Q_1 = 2.06\ \mathrm{J/g\cdot^{\circ}C} \cdot 20\ \mathrm{g} \cdot 50^{\circ}\mathrm{C} = 2.06\ \mathrm{kJ} \\ Q_2 = 334\ \mathrm{J/g} \cdot 20\ \mathrm{g} = 6.68\ \mathrm{kJ} \\ Q = 2.06 + 6.68 = 8.74\ \mathrm{kJ}. \end{array}$$

**Answer:** $8.74\ \mathrm{kJ}$.

3. Under certain conditions, nitrogen gas and oxygen gas react to form the toxic brown gas nitrogen dioxide: $\mathrm{N2(g)} + 2\ \mathrm{O2(g)} \longrightarrow 2\ \mathrm{NO2(g)}$. For this reaction, triangle $\mathrm{H}^{\circ} = 66.2\ \mathrm{kJ}$ and triangle $\mathrm{S}^{\circ} = -121.81\ \mathrm{J/K}$; calculate triangle $\mathrm{G}^{\circ}$ at standard conditions (298 K and 1 atm) and determined if a reaction is spontaneous, nonspontaneous, or an equilibrium at these conditions.

**Solution:**

$$\begin{array}{l} \Delta G = \Delta H - T \cdot \Delta S \\ \Delta G = 66200 - 298 \cdot (-121.81) = 102500\ \mathrm{J} = 102.5\ \mathrm{kJ}. \end{array}$$

$\Delta G > 0$, so the reaction is nonspontaneous.

**Answer:** $102.5\ \mathrm{kJ}$, the reaction is nonspontaneous.

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