Written assignment 4: chemical reactions


Written Assignment 4: Chemical Reactions

Answer all assigned questions and problems, and show all work. 

1. Write the (a) balanced equation for the formation of liquid water from hydrogen and oxygen gas, and use it to explain the following terms: (b) chemical reaction, (c) reactant, (d) product. (12 points)

2. Balance the following equations: (18 points)

  1. 2C + O2 2CO
  2. 2CO + O2 2CO2
  3. 2Na + 2H2O H2 + 2NaOH
  4. Zn + 2HCl ZnCl2 + H2
  5. 2NaOH + H2SO4 2H2O + Na2SO4
  6. 2NH3 + 3CuO 3Cu + N2 + 3H2O

3. Calculate the mass in grams of iodine (I2) that will react completely with 20.4 g of aluminum (Al) to form aluminum iodide (AlI3). (5 points)

(Reference: Chang 3.47)

4. The annual production of sulfur dioxide from burning coal and fossil fuels, auto exhaust, and other sources is about 26 million tons. The equation for the reaction is

S(s) + O2 (g) → SO2 (g)

How much sulfur (in tons), present in the original materials, would result in that quantity of SO2? (5 points)


(Reference: Chang 3.69)

5. Each copper (II) sulfate unit is associated with five water molecules in crystalline copper(II) sulfate pentahydrate (CuSO4 ⋅ 5H2O). When this compound is heated in air above 100oC, it loses the water molecules are also its blue color:

CuSO4 ⋅ 5H2O → CuSO4 + 5H2O

If 9.60 g of CuSO4 are left after heating 15.01 g of the blue compound, calculate the number of moles of water originally present in the compound. (5 points)

(Reference: Chang 3.73)

6. The fertilizer ammonium sulfate [(NH4)2SO4] is prepared by the reaction between ammonia (NH3) and sulfuric acid:

2 NH3(g) + H2SO4(aq)  → (NH4)2SO4(aq)

How many kilograms of NH3 are needed to produce 1.00 × 105 kg of (NH4)2SO4?


(5 points)

(Reference: Chang 3.77

7. Nitric acid (NO) reacts with oxygen gas to form nitrogen dioxide (NO2), a dark brown gas:

2NO(g) + O2(g) → 2NO2(g)

In one experiment 0.886 mole of NO is mixed with 0.503 mol of O2. 

  1. Calculate which of the       two reactants the limiting reagent is. (5 points) 
  2. Calculate also the number of moles of NO2       produced. (5 points)
  3. What reactant is left       over and how much of it is left over? (5 points)

(Reference: Chang 3.83)

8. Propane (C3H8) is a component of natural gas and is used in domestic cooking and heating. It burns according to the following reaction:

C3H8 + 5O2 → 3CO2 + 4H2O

  1. Balance the equation representing the       combustion of propane in air. (5       points)
  1. How many grams of       carbon dioxide can be produced by burning 20.0 pounds of propane, the       typical size of a BBG grill propane tank? Assume that oxygen is the excess reagent in this reaction. (5 points)

9. Hydrogen fluoride is used in the manufacture of Freons (which destroy ozone in the stratosphere) and in the production of aluminum metal. It is prepared by the reaction

CaF2 + H2SO4 → CaSO4 + 2HF

In one process 6.00 kg of CaF2 are treated with an excess of H2SO4 and yield 2.86 kg of HF. Calculate the percent yield of HF. (5 points)

(Reference: Chang 3.89)

10. Certain race cars use methanol (CH3OH; also called wood alcohol) as a fuel. Methanol has a molecular mass of 32.0 g/mol and a density of 0.79 g/mL. The combustion of methanol occurs according to the following equation:

2CH3OH + 3O2 → 2CO2 + 4H2O

In a particular reaction 2.00 L of methanol are reacted with 80.0 kg of oxygen.


  1. What is the limiting reactant? (5       points) 
  2. What reactant and how many grams of it are left over? (5 points) 
  3. How many grams of carbon dioxide is produced? (5 points)

11. An iron bar weighed 664 g. After the bar had been standing in moist air for a month, exactly one-eighth of the iron turned to rust (Fe2O3). Calculate the final mass of the iron bar and rust. (5 points)

(Reference: Chang 3.111)

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