# 2.7 Practice Problems

 1. Calculate the kinetic energy of an oxygen atom moving at a speed of $\pu{100 m s−1}$. Hint: convert mass of an $\ce{O}$ atom from $\pu{amu}$ to $\pu{g}$. 
 2. Calculate $\Delta_{rxn}H^\circ$ for the following reactions using thermodynamic data:

$$\begin{align*}
\ce{H2 + F2 &-> 2 HF\\
2 NO2 &-> N2O4
}
\end{align*}$$
3. How is the system defined in this chemical reaction? Where does the energy go?
4. According to a Clif Bar nutrition label, it contains $\pu{240 Cal}$ of energy. How much is this energy in $\pu{J}$?
5. What would be good examples of open, closed, and isolated systems in nature? 
6. Of mass and concentration, which property is conserved in a system?
7. Is a mixture of different gases a single phase?
8. What component defines a pure $\ce{H2O}$ system?
9. What component(s) defines an aqueous system composed of $\ce{CO2}$ and $\ce{CaCO3}$?
10. How many properties are required to define a system of $\pu{1 L}$ pure $\ce{H2O}$?
11. If $\Delta_{rxn}H^\circ = \pu{2803 kJ mol-1}$ for photosynthesis reaction shown in the reaction below. Calculate the solar energy required to produce $\pu{75 g}$ of $\ce{C6H12O6}$.

$$\ce{6 H2O(l) + 6 CO2(g) ->[Sunlight] C6H12O6(s) + 6 O2(g)}$$

12. If $\Delta_{rxn}H^\circ = \pu{-72.4 kJ mol-1}$ for the reaction shown below. Calculate the heat released when $\pu{1 kg}$ of $\ce{Br2}$ is consumed in this reaction.

$$\ce{H2(g) + Br2(l) -> 2 HBr(g)}$$

13. If $\Delta_{rxn}H^\circ = \pu{333.8 kJ mol-1}$ for the thermochemical equation shown below, calculate the mass of copper produced when $\pu{1.47e4 kJ}$ is consumed in this reaction.

$$\ce{2 Cu2O -> 4 Cu + O2}$$

14. Determine the enthalpy change for each reaction using the reaction data provided in the table below each reaction:

$$\ce{NO(g) + O(g) -> NO2(g)}$$

| Reaction      | $\Delta_{rxn}H^\circ$, $\pu{kJ mol-1}$ |
|-------------------------|------:|
| $\ce{NO(g) + O3(g) -> NO2(g) + O2 (g)}$ | $-198.9$  |
| $\ce{O3(g)  -> 3/2 O2 (g)}$ | $-142.3$ |
| $\ce{O2(g) -> 2 O (g)}$  | $-571.6$ |

$$\ce{
3 H2 + O3 -> 3 H2O
}$$

| Reaction      |  $\Delta_{rxn}H^\circ$, $\pu{kJ mol-1}$ |
| ------------- | -------------: |
| $\ce{2 H2 (g) + O2(g) -> 2H2O (g)}$ | $-483.6$|
| $\ce{3 O2(g) -> 2 O3 (g)}$ | $284.6$ |

$$ \ce{
P4O6 + 2 O2 -> P4O10}
$$

| Reaction   | $\Delta_{rxn}H^\circ$, $\pu{kJ mol-1}$ |
|--------------|-----------------: |
| $\ce{P4 (s) + 3 O2(g) -> P4O6 (s)}$ | $-1640.1$ |
|  $\ce{P4(s) + 5O2(g) -> P4O10(s) }$ | $-2940.1$ |

15. Calculate $\Delta_{rxn}S^\circ$of the following reactions at $\pu{25 ^\circ C}$:

$$
\begin{align*}
\ce{
N2 + 3 H2 &-> 2 NH3\\
H2 + Cl2 &-> 2 HCl\\
H2 + CuO &-> Cu + H2O\\
2 Al + 3 ZnO &-> Al2O3 + 3 Zn\\
CH4 + 2 O2 &-> CO2 + 2 H2O
}
\end{align*}
$$

16. Determine the sign of $\Delta_{sys}S$ for the following systems using the rules outlined in the section on [the qualitative prediction entropy of substances](https://vijayvulava.github.io/geochem/24SecondLaw.html#qualitative-prediction-of-delta-sys-s-circ):
	1. Freezing ethanol
	2. Evaporating water
	3. Heating water
	4. Condensing bromine vapor

17. Calculate $\Delta_{rxn}G^\circ$ for the following reactions at $\pu{25 ^\circ C}$:

$$
\begin{align*}
\ce{
2 MgO &-> 2 Mg + O2\\
H2 + Br2 &-> 2 HBr\\
2 C2H6 + 7 O2 &-> 4 CO2 + 6 H2O
}
\end{align*}
$$

18. Determine the $T$ at which the following reactions reach equilibrium:

$$
\begin{align*}
\ce{
2 MgO &-> 2 Mg + O2\\
H2 + Br2 &-> 2 HBr\\
2 C2H6 + 7 O2 &-> 4 CO2 + 6 H2O
}
\end{align*}
$$