When we have gases in chemical reactions, we may need to use the ideal gas law first to find the moles of gas as a start to our dimensional analysis. Or we could use dimensional analysis first to find the moles of gas and the ideal gas law second to find a different variable for the gas. Let's practice with gases in chemical reactions and stoichiometry. Our problem reads, "In the following reaction, 4.58 liters of oxygen was formed at 745 millimeters of mercury and 308 Kelvin. How many grams of silver oxide decomposed?" In this problem, we'll first use the ideal gas law to find moles of oxygen gas. Then we'll use dimensional analysis to convert to grams of silver oxide. We can rearrange the ideal gas law to solve for moles. When we plug our pressure into the ideal gas law, we need to convert from millimeters of mercury into atmospheres using 1 atmosphere is equal to 760 millimeters of mercury. Completing the calculation, we get 0.178 moles of oxygen. Next, we'll use dimensional analysis to convert from moles of oxygen to grams of silver oxide. We can use the coefficients in the balanced chemical equation to convert from moles of oxygen to moles of silver oxide. And we can use the molar mass of silver oxide to convert from moles to grams. Completing the calculation, we should get 82.3 grams of silver oxide.