Question 6.10: Applying the Law of Combining Volumes Zinc blende, ZnS, is t...
Applying the Law of Combining Volumes
Zinc blende, ZnS, is the most important zinc ore. Roasting (strong heating) of ZnS in oxygen is the first step in the commercial production of zinc.
2 ZnS(s) + 3 O_2 (g) \xrightarrow{\Delta} 2 ZnO(s) + 2 SO_2 (g)
What volume of SO_2 (g) can be obtained from 1.00 L O_2 (g) and excess ZnS(s)? Both gases are measured at 25 °C and 745 mmHg.
Analyze
The reactant and product being compared are both gases, and both are at the same temperature and pressure. Therefore, we can use the law of combining volumes and treat the coefficients in the balanced chemical equation as if they had units of liters.
The stoichiometric factor (shown below in blue) converts from L O_2 (g) to L SO_2 (g).
? L SO_2 (g) = 1.00 L O_2 (g) \times \frac{2 L SO_2 (g)}{3 L O_2 (g)} = 0.667 L SO_2 (g)
Assess
Some students would solve this problem by using the following sequence of conversions: L O_2 \longrightarrow mol O_2 \longrightarrow mol SO_2 \longrightarrow L SO_2. This approach is acceptable but not as simple as the approach we used.