Practice Midterm 2 Problems

Practice Midterm 2 Problems Ch 5, 6, 7

Acetylene, C2H2, is produced by the reaction:

CaC2(s) + 2H2O(l) → C2H2(g) + Ca(OH)2(aq)

This reaction is carried out and the acetylene is collected by the displacement of water. If 385 mL of gas is produced at 23 ºC and an atmospheric pressure of 750 torr, how many moles of acetylene were formed? (the vapor pressure of water at 23 ºC is 21 torr)

A gaseous mixture of nitrogen and helium is 50% helium by mass. If the total pressure is 500 torr, calculate the partial pressure of each gas.

A 250 mL sample of tetrahydrocannibol gas at STP has a mass of 3.65 g. What is the molar mass of THC?

A compound has the empirical formula CHCl. A 256 mL flask at 373 K and 750 torr contains 0.800 g of the gaseous compound. Give the molecular formula.

Calculate the pressure of exerted by 50.0 g of nitrous gas in a 1.00 L container at 25.0 °C. Assume that nitrous is not an ideal gas under these conditions. (a= 5.284 atm L2 mol-2, b = 0.04424 L mol-1)

What do the “a” and “b” constants mean in the van der Waals equation? Which would have a bigger “a” value, H2O or He? What about the “b” value for those gases?

A 2.50 L sample of butane gas at a pressure of 1.00 atm is compressed into a lighter which is then used by MacGyver to ignite a bomb made from an oil can, a pair of pantyhose, an exhaust pipe and a battery. If the volume of the lighter is 5.20 mL, what is the pressure of the butane in the lighter?

Under which conditions does a gas behave most ideally?

For the following, compare a sample of H2(g) and CO2(g), both 1.0 L, 1.0 atm and 25 °C.

a. Which has the higher density?

b. In which are the molecules moving faster?

c. Which has the greater number of molecules?

d. Which has the highest average kinetic energy?

It took 4.5 minutes for 1.0 L helium to effuse through a porous barrier. How long will it take for 1.0 L Cl2 gas to effuse?

A 2.00 L sample of methane gas at a pressure of 2.50 atm is compressed to a volume of 0.250 L at constant temperature. What is the new pressure of the methane?

Write the equilibrium expression for the following reactions:

a. NH4NO3(s) → N2O(g) + 2H2O(g)

b. H3O+(aq) + OH-(aq) → 2H2O(l)

For the following reaction at 25 °C N2(g) + 3H2(g) → 2NH3(g), Kc = 3.5 x 108. Calculate Kp.

Consider the reaction H2(g) + I2(g) → 2HI(g) . Hydrogen and iodine are placed in a sealed flask at initial concentrations of 0.0175 mol/L each. When the system comes to equilibrium, the concentration of hydrogen iodide is 0.0276 mol/L. Calculate K for this reaction.

Consider the same reaction as above. For the following conditions, determine if the reaction is at equilibrium, and if it isn’t, indicate the direction it will shift to reach equilibrium.

a. PH2 = 0.050 atm, PI2= 0.075 atm, PHI = 1.20 atm

b. [H2] = 2.00 M, [I2] = 0.90 M, [HI] = 0.015 M

To an evacuated container, NO and Br2 are added at a pressure of 0.34 atm each. They react according to the following equation. At equilibrium the total pressure is 0.62 atm. Calculate Kp for the reaction.

2NO(g) + Br2 (g) → 2NOBr (g)

Solid NH4HS is placed into an evacuated, closed container and allowed to come to equilibrium. Calculate the total pressure at equilibrium.

NH4HS (s) → NH3 (g) + H2S (g) Kp = 0.070

Consider the following reaction, which is endothermic:

2SO2(g) + O2(g) 2SO3(g)

How will each of the following affect the equilibrium?

a. oxygen gas is added

b. the reaction is heated

c. the volume of the reaction vessel is doubled

d. the total pressure of the system is increased by adding a noble gas

e. SO3(g) is removed

Given the following exothermic reaction at equilibrium, how will the following affect it?

PCl5 (s) → PCl3(g) + Cl2(g)

a. chlorine gas is added

b. the total pressure is increased by adding argon gas

c. the total pressure is increased by decreasing the volume of the container

d. PCl3 is removed

e. PCl5 is added

f. the temperature is increased

Consider the reaction H2(g) + I2(g) → 2HI(g) . At equilibrium, the concentrations are hydrogen 0.010 M, iodine 0.010 M and hydrogen iodide 0.074 M. If the concentration of hydrogen iodide is increased to 0.10 M, what will be the final concentrations of all species once equilibrium is reestablished?

Calculate the pH of the following solutions:

a. 1.28 M HCl

b. 0.50 M CH3COOH (Ka = 1.8 x 10-5)

c. 3.00 M NaOH

d. 1.87 M CH3NH2 (Kb = 4.38 x 10-4)

e. 1.00 M NaCl

f. 0.85 M KNO2 (Ka (HNO2) = 4 x 10-4)

g. 0.73 M NH4NO3 (Kb (NH3) = 1.8 x 10-5)

Calculate the pH of a 5.0 M H3PO4 solution and determine the equilibrium concentrations of the species H3PO4, H2PO4-, HPO42- and PO43-.

(Ka1= 7.5 x 10-3, Ka2 = 6.2 x 10-8, Ka3 = 4.8 x 10-13)

What volume of 0.0521 M Ba(OH)2 is required to neutralize 14.20 mL of 0.141 M H3PO4? Phosphoric acid contains three acidic hydrogens.

Calculate the concentration of H+ in solution if 30.0 mL of 0.0521 M Ba(OH)2 are added to the same solution of phosphoric acid above.