Stoichiometry
For the reaction 2 X₂ + 3 Y₂ → 2 X₂Y₃, a particle diagram shows 8 molecules of X₂ and 9 molecules of Y₂ before the reaction. If the reaction goes to completion, which reactant is limiting, how many molecules of X₂Y₃ form, and what remains?
Y₂ is limiting. 6 molecules of X₂Y₃ form, and 2 molecules of X₂ remain.
A reaction has ΔH = −245 kJ. Is the reaction endothermic or exothermic, and is heat absorbed or released?
Exothermic; heat is released.
How many moles of NaCl are present in 35.0 mL of a 0.120 M NaCl solution?
0.00420 mol NaCl
According to kinetic molecular theory, why does pressure increase when a gas is heated in a rigid container?
The particles move faster, hit the container walls more often, and hit with greater force.
Write the equilibrium expression for the reaction 2 NO₂(g) ⇌ N₂O₄(g).
Keq = [N₂O₄] / [NO₂]²
Question: For the reaction 3 Mg + N₂ → Mg₃N₂, how many moles of Mg₃N₂ can form from 7.50 mol Mg and excess N₂?
2.50 mol Mg₃N₂
A 18.0 g metal sample absorbs 376 J of heat. Its temperature increases from 22.0°C to 57.0°C. What is the specific heat capacity of the metal?
0.597 J/g°C
A solution is made by dissolving 16.5 g of KBr in enough water to make 150.0 g of total solution. What is the percent by mass of KBr?
11.00%
A gas has a volume of 4.00 L at 1.20 atm. The temperature stays constant, and the gas is compressed to 2.50 L. What is the new pressure?
1.92 atm
For the equilibrium CO(g) + 2 H₂(g) ⇌ CH₃OH(g) + heat, which direction will the system shift if temperature is increased?
Left, toward the reactants.
Potassium chlorate decomposes according to the equation 2 KClO₃ → 2 KCl + 3 O₂. If 14.8 g of KClO₃ decomposes completely, how many grams of O₂ form? Molar mass: KClO₃ = 122.55 g/mol; O₂ = 32.00 g/mol.
5.80 g O₂
On a heating curve, the temperature stays constant during a flat section while heat is still being added. What is happening to the energy during that flat section?
The energy is being used for a phase change, not to increase temperature.
A student dilutes 50.0 mL of 0.800 M NaOH to a final volume of 200.0 mL. What is the final concentration?
0.200 M NaOH
A balloon has a volume of 3.50 L at 15.0°C. The pressure stays constant, and the temperature increases to 45.0°C. What is the new volume?
3.86 L
n the reaction HCO₃⁻ + H₂O ⇌ H₃O⁺ + CO₃²⁻, identify the acid and its conjugate base.
HCO₃⁻ is the acid, and CO₃²⁻ is its conjugate base.
Calcium carbonate decomposes according to the equation CaCO₃ → CaO + CO₂. If 12.5 g of CaCO₃ should produce 7.00 g of CaO theoretically, but the experiment produces 6.10 g of CaO, what is the percent yield?
87.14%
A 18.0 g sample of ice starts at −10.0°C and is heated until it becomes liquid water at 0.0°C. Use cice = 2.09 J/g°C, ΔHfus = 6.01 kJ/mol, and molar mass H₂O = 18.02 g/mol. What is the total enthalpy change?
6.38 kJ
Which 0.200 m solution would have the lowest freezing point: C₆H₁₂O₆, NaCl, MgCl₂, or AlCl₃?
AlCl₃, because it produces the most dissolved particles.
A gas mixture has a total pressure of 3.65 atm. The partial pressure of nitrogen is 1.20 atm, and the partial pressure of oxygen is 0.850 atm. What is the partial pressure of argon?
1.60 atm
A solution has [H⁺] = 6.3 × 10⁻⁴ M. What is the pH?
3.20
Nitrogen gas reacts with hydrogen gas according to the equation N₂ + 3 H₂ → 2 NH₃. If 10.0 g of N₂ reacts with 2.00 g of H₂, what mass of excess reactant remains after the reaction is complete? Molar masses: N₂ = 28.02 g/mol; H₂ = 2.016 g/mol.
0.734 g N₂ remains
Use the reactions below to find ΔH for the target reaction.
Target reaction: 2 NO(g) + O₂(g) → 2 NO₂(g)
Given:
N₂(g) + O₂(g) → 2 NO(g) ΔH = +180.5 kJ
N₂(g) + 2 O₂(g) → 2 NO₂(g) ΔH = +66.4 kJ
−114.1 kJ
Solutions of calcium nitrate and sodium carbonate are mixed. A precipitate of calcium carbonate forms. What is the net ionic equation?
Ca²⁺(aq) + CO₃²⁻(aq) → CaCO₃(s)
A gas sample has a volume of 2.80 L at 0.950 atm and 18.0°C. The gas is moved to a container where the pressure is 1.25 atm and the temperature is 42.0°C. What is the new volume?
2.30 L
A student titrates 15.0 mL of H₂SO₄ with 0.120 M NaOH. It takes 28.4 mL of NaOH to reach the equivalence point. What is the molarity of the H₂SO₄?
H₂SO₄ + 2 NaOH → Na₂SO₄ + 2 H₂O
0.114 M H₂SO₄