Gas Stoichiometry
Student Expectation
The student is expected to perform stoichiometric calculations, including determination of mass and volume relationships between reactants and products for reactions involving gases.
Key Concepts
A balanced chemical equation, stoichiometric ratios, and molar masses may be used to determine the mole and mass relationships between the amounts of products and reactants in a chemical equation involving gases.
When a chemical reaction involves gases at constant pressure and temperature, the coefficients of a balanced chemical equation may be used to represent stoichiometric mole and/or volume ratios. For reactions occurring at STP, the conversion between moles and liters is 22.4 L per 1 mol for all gases. For reactions not at STP, stoichiometric ratios along with the ideal gas law can be used to determine mole and volume relationships between amounts of products and reactants in the chemical equation.
GAS STOICHIOMETRY
Calculating Quantities and Relationships Involving Gases
In chemical equations involving gases, balanced chemical equations, stoichiometric ratios, and molar masses may be used to determine the mole and mass relationships between the products and reactants.
Using the Ideal Gas Law
The ideal gas law is represented by the equation:
PV = nRT
P is gas pressure, V is its volume, n is number of moles, R is the ideal gas constant, and T is gas temperature. Integrating Boyle’s law, Charles' law, and Avogadro’s law, the ideal gas law explains the relationship between these factors described above.
For instance, if 620 mL gas of HCl is dissolved in water making 1000 mL of solution at 200 kPa and 273 K, what is the solution’s concentration?
Calculate Number of Moles: In this problem, we need to calculate number of moles for the HCl gas first. Making use of the ideal gas law, as follows:
n = (PV) / (RT)
n = (200 kPa x 0.620 L) / ((8.314 kPa•L / K•mol) x 273 K) = 0.0546 mol
Calculate Concentration of the Solution: The second step is to figure out the concentration of the solution. Concentration is represented by the chemical formula of the solute surrounded by brackets. [HCl] means “concentration of hydrochloric acid.” Concentration is represented as moles per unit volume, thus:
[HCl] = 0.0546 mol / 1.00 L = 0.0546 mol/L
From this example, we learned how to utilize the ideal gas law to capture certain parameters for gas, such as the number of moles of HCl. In addition, we calculated the concentration of solution.
For Reactions at STP
When a chemical reaction involves gases at constant pressure and temperature, the coefficients of a balanced chemical equation may be used to represent stoichiometric mole and/or volume ratios. Standard temperature and pressure (STP) is 0°C (273 K) and 1.0 atm. For reactions occurring at STP, the conversion between moles and liters is 22.4 L = 1 mol for all gases.
For Reactions Not at STP
For reactions not at STP, stoichiometric ratios, along with the ideal gas law, can be used to determine mole and volume relationships between amounts of products and reactants in the chemical equation.