Gas Laws
The "R" stands for this in the ideal gas law equation PV = nRT
What is the ideal gas constant (0.0821 L·atm/mol·K)
What is the first step in any stoichiometric calculation?
Balance the chemical equation.
What is a limiting reactant?
The reactant that runs out first and limits the reaction.
What kind of reaction is this: AB → A + B?
Decomposition
Name one safety rule you must follow in a chemistry lab.
Wear goggles, tie back hair, no eating, etc.
Convert 25°C to Kelvin.
298 K
Define "mole ratio."
The ratio of coefficients from a balanced equation.
Why is identifying the limiting reactant important?
It determines how much product is formed.
How can you tell a chemical reaction has occurred? Name two possible signs.
Color change, temperature change, gas production, precipitate formation, or light emission.
What should you do if your data doesn’t match your calculations?
Recheck work, analyze sources of error.
A gas occupies 2.0 L at 1 atm and 273 K. What is the number of moles?
n = PV/RT = (1×2)/(0.0821×273) ≈ 0.089 mol
Convert 36 g of water (H₂O) to moles.
36 g ÷ 18.02 g/mol = 2.00 mol
If you have 4 mol A and 5 mol B for the reaction A + 2B → C, which is limiting?
B is limiting (needs 8 mol, but only 5 are available).
What do coefficients in a balanced equation represent?
Mole ratios
What should you check first if a gas-collecting reaction produces no visible change?
Check that the reactants were mixed properly, equipment was sealed, and the reaction setup was correct (no leaks or missing materials)
What happens to volume if temperature increases at constant pressure?
Volume increases (direct relationship – Charles's Law)
In the reaction 2H₂ + O₂ → 2H₂O, how many moles of O₂ are needed for 4 mol H₂?
2 mol O₂
How can you experimentally tell which reactant is in excess?
Excess will be left unreacted at the end.
Write the balanced equation for the combustion of methane.
CH₄ + 2O₂ → CO₂ + 2H₂O
What factors could cause lower-than-expected product amounts?
Incomplete reaction, leaks, measurement error.
A sample of gas at 1.5 atm and 305 K occupies 0.750 L. Solve for n.
n = PV/RT ≈ (1.5×0.75)/(0.0821×305) ≈ 0.045 mol
Given 3.0 mol of A in the reaction A + 2B → 3C, how many mol of C?
3.0 mol A × (3 mol C / 1 mol A) = 9.0 mol C
Describe how to determine the limiting reactant using stoichiometry.
Convert both reactants to moles of product and see which makes less.
Why must equations be balanced?
To obey the law of conservation of mass.
What makes an experimental design “optimal”?
It meets the goal efficiently and with minimal waste.