Cornell Invitational — Chemistry Lab Written Portion

Hydrogen peroxide decomposes into H₂O(l) and O₂(g). What volume of O₂ is collected at 27.0°C and 740. torr if only half the 130g of hydrogen peroxide decompose? (Ignore presence of water vapor)

A solution of BaF₂ which has a density of 4.89 g/mL is 20% barium ions by mass. What is the moles of fluoride ions in 150 mL of solution?

A sealed flask which is 22.4 L contains an ideal gas at STP. How many moles of gas are contained?

There are two balloons sitting on a lab bench under the same conditions. One contains 6.0 g of H₂(g) while the other 96 g of O₂(g). How do the two balloons compare?

A 0.150 L sample of gaseous hydrocarbon has a density of 0.582 g/L at 76°C and 790 torr. What is its formula?

An equimolar mixture of C₂H₆ and C₅H₁₂ diffuses through a pinhole. What is ratio of C₂H₆/C₅H₁₂ that escapes?

The Kinetic molecular theory describes the behavior of ideal gases. Real gases deviate from these postulates. Under what conditions do real gases deviate most from the theory?

An apparatus contains Br₂(g) in a solution. What happens to vapor pressure when the piston lowers and decreases the volume of Br₂(g) above the solution by half? (Assume no temperature change).

What is the average velocity of H₂ molecules at 60 K relative to their velocity at 120 K?

0.100L of N₂(g) takes 220s to completely diffuse through a pinhole. Under the same temperature and pressure, 0.100 L of unknown gas takes 300s to completely diffuse through the same pinhole. What is the molar mass of the unknown gas?

What is the total pressure in a 2.00 L container that holds 1.00 g H₂, 2.00 g He, and 16.0 g of CO at 26.0°C?

Hydrogen gas is collected over water at 43°C and 740 mmHg. Water has a vapor pressure of 65 mmHg at 43°C. If 250 mL of hydrogen gas is collected, what portion of the volume is the dry form of this gas under the same temperature and pressure?

A sealed flask contains an ideal gas. The 15 L flask is initially at 100 K and 20 atm. When the flask is heated, it reaches a pressure of 300 atm. What is its final temperature?

A container contains equal amounts by mass of gaseous O₂, H₂O, and CO₂ for a total pressure of 3 atm. How do the partial pressures of gaseous O₂, H₂O, and CO₂ compare?

2.00 g of water is introduced to a 4.00 L evacuated flask at 298 K. The vapor of water at 298 K is 83.8 torr. What is the mass of liquid water when equilibrium was reached?

Gaseous SO₂ does not behave exactly like an ideal gas. Its collisions are not perfectly elastic. Using the ideal gas equation, a student obtains the pressure of a sample of SO₂(g). How does the actual pressure of the sample deviate?

Approximately how many times faster will a molecule of hydrogen gas effuse than an atom of radon?

What is special about liquid water compared to other substances of similar molar masses?

1. Low boiling point
2. High melting point
3. Large specific heat capacity
4. Large surface tension

What does liquid CH₂N₂ need to overcome to evaporate? I. Van der Waals forces II. Dipole-dipole forces III. Attractive forces with air

In 2.0 L container, a sample of natural gas contains only methane and ethane. The mole ratio of methane is 0.877. What is the partial pressure of ethane at 1.5 atm and 22°C?

Which of the pure substances have the highest normal boiling point?

The kinetic energy of the molecules in a sample of water in its stable state at 1 atm and -8°C doubles. What are the initial and final phases?

What is the change in volume when 20.0g carbon dioxide sublimes at 25°C in a pistol at 1.0 atm? (Neglect volume of solid CO₂)

The reaction between iron and hydrochloric acid is Fe(s) + 2HCl(aq) → FeCl₂(aq) + H₂(g). How many kilograms of iron was needed to produce 2000. L of H₂ at 2.5 atm and 52°C? (Ignore the vapor pressure of HCl and FeCl₂)

Acetone and benzene form an ideal solution when mixed. Acetone has a vapor pressure of 214 torr at 25°C and benzene has a vapor pressure of 96 torr at 25°C. What is the vapor pressure of the solution with equal amounts by moles of acetone and benzene (the mole fraction of both is 0.5)?

Which physical property increases when intermolecular forces increase? i. boiling point ii. surface tension iii. viscosity

Which of the following laws do not relate to forming the ideal gas equation?

A bomb calorimeter contains 150. g of water. The calorimeter has a heat capacity of 567 J·°C⁻¹ and water has a specific heat of 4.184 J·g⁻¹·°C⁻¹. How much heat, in kilojoules, is evolved when temperature of the system increases from 24.54°C to 27.01°C?

Consider this reaction and the enthalpy value. H₂(g) + ½ O₂(g) → H₂O(l) ΔH°_f = -286 kJ/mol Which of the following statements is incorrect?

Calculate the enthalpy of reaction when 2.0 g of S react with 5.0 g of O₂. S(s) + O₂(g) → SO₂(g) ∆H˚_f = -296.8 kJ/mol

A process that is exothermic and nonspontaneous could be the following:

Gibbs free energy, ΔG, is the free energy of the system used to do work. The sign of ΔG determines the favorability of a reaction. For which reaction will ΔG decrease the most when temperature of the system decreases from 32 °C to 0 °C?

Consider the balanced reaction: 4 NH₃(g) + 5 O₂(g) → 4 NO(g) + 6 H₂O(g) ΔH° = -904.4 kJ Calculate ΔH°_f of NO(g) in kJ/mol. (ΔH°_f for NH₃ = -46.2 kJ/mol, ΔH°_f for H₂O(g) = -241.8 kJ/mol)

Calculate the ΔH°_{rxn} for the following ΔH°_f values: H₂O(l) = -285.8 kJ/mol, CH₄ = -74.8 kJ/mol, CO(g) = -110.5 kJ/mol H₂O(l) + CH₄ → CO(g) + 3H₂(g)

30.0 mL of 0.100 M HNO₃ titrates 30.0 mL of 0.100 M KOH. The temperature of solution rises by 2.0°C. What is the enthalpy of neutralization per mole of HNO₃? (C_P = 4.18 J·g⁻¹·°C⁻¹, density = 1.0 g/mL)

Which of the following substance has the highest entropy value, S˚, at 25 ˚C?

For the reaction, CaCO₃(s) → CO₂(g) + CaO(s), which of the following is not always true?

The combustion of 92 g of liquid C₂H₅OH produces CO₂(g) + H₂O(l). What is the enthalpy of combustion for C₂H₅OH(l)? (ΔH°_f for H₂O(l) = -285.8 kJ/mol, ΔH°_f for CO₂(g) = -393.5 kJ/mol, ΔH°_f for C₂H₅OH(l) = -277.7 kJ/mol)

The reaction 2SO₂(g) → S₂O₄(g) has a ∆H < 0. For the reaction to be spontaneous, which of the conditions must be true?

For which reaction is ∆H closest to ∆E (internal energy)?

What is the relationship between S˚ and temperature?

For the reaction at 25°C, 2C₂H₆(l) + 7O₂(g) → 4CO₂(g) + 6H₂O(g), what expression gives the ∆H?

You dissolve 6.98 g NaCl in 150 g of water at room temperature (25°C). Find the final temperature of the solution. (Molar mass NaCl = 58.44 g/mol, ∆H_soln/NaCl = 21.2 kJ/mol, C_P,solution = 4.184 J·g⁻¹·°C⁻¹)

Benzene boils at 80.1°C with ∆H°{vap} = 30.77 kJ/mol. What is the ∆S°{vap} in J·mol⁻¹·K⁻¹?

In a bomb calorimeter, what thermodynamic quantity is used to measure heat of reaction?

The specific heat of Ni is 0.440 J·g⁻¹·°C⁻¹ and the specific heat of water is 4.184 J·g⁻¹·°C⁻¹. If 90.7 g of nickel at 110°C is dissolved in 106.4 g of water at 27°C, what is the final temperature of the system?

12 g of unknown metal heated at 75.0˚C is placed in 0.100 L water at 21.0˚C. When the system has reached equilibrium, the final temperature of the system is 22.4˚C. Based on the specific heat of the metal, find its identity?

Determine the molar bond enthalpy for the reaction, H₂ + Cl₂ → 2HCl.

Molar bond enthalpies (kJ/mol) H-Cl 431 H-H 435 Cl-Cl 243

Calculate ∆H˚_f for the reaction: Zn(s) + H₂S(g) → H₂(g) + ZnS(s) (∆H˚_f for H₂S = -20.6 kJ/mol, ∆H˚_f for ZnS = -206.0 kJ/mol)

Use bond energies and ∆H˚{rxn} to estimate the molar bond energy for C-Br: CF₄ + 2 Br₂ → CBr₄ + 2 F₂ ∆H˚{rxn} = 892 kJ

At 1 atm, which is the correct relationship for this equation: C(s) + 2S(s) → CS₂(g) ∆H˚ = 92 kJ

At standard pressure, if enthalpy is positive, what temperature is needed for this reaction to be spontaneous?

A 3.0 L container is filled with gas. The external pressure, outside the container, is 0.80 bar. If the energy change is 500 J, how much heat is the surroundings giving the container? (100 J = 1 L-bar)

Which statement about phase diagrams is correct?

Ethane melts at 90.0 K and its enthalpy of fusion is 2.85 kJ/mol. What is the entropy of fusion (J/mol-K) for ethane?

How many kilojoules of energy is needed to melt 25 g of ice at 0°C into liquid water at 21°C? (ΔH°_{fusion} for H₂O is 333.5 kJ/kg and C_P,liquid is 4.18 J·g⁻¹·°C⁻¹)

What is the second law of thermodynamics?