CHM 1045
Dr. Michael Blaber

Name_________________________

SS #__________________________

1. A helium atom is moving at 9/10^th’s the speed of light, and a Sulfur atom is moving at ½ the speed of light. Which atom has the highest kinetic energy, and what is that kinetic energy in Joules? (1 point)

Helium: ½mv² = ½*(4.0*1.66 x 10^-24g)*(1 kg/1000g)*(0.9*3 x 10⁸ m/s)² = 2.42x10^-10 J

Sulfur: ½mv² = ½*(32.1*1.66 x 10^-24g)*(1 kg/1000g)*(0.5*3 x 10⁸ m/s)² = 5.99x10^-10 J

Sulfur atom has highest kinetic energy

2. A certain sample of iron requires 87 Joules to raise its temperature from room temperature (298K) to body temperature (310K). How many moles are in the sample of iron? (The specific heat of iron is 0.45 J g^-1 K^-1). (1 point)

Grams of substance = (quantity of heat transferred)/(temperature change * specific heat)

= 87 J / (12 K * 0.45 J g^-1 K^-1) = 16.1 g

16.1 g (1 mole/55.8g) = 0.289 moles

3. 200 mls of an aqueous solution of hydrofluoric acid (HF) and 37 mls of potassium hydroxide (KOH) are allowed to react in a constant pressure calorimeter. After the reaction it is noted that the solution has increased its temperature from 298K to 333K. Calculate the enthalpy change for the reaction. (assume density and specific heat of the solution is the same as for water) (1 point)

DT solution = 35K

specific heat = 4.18 J g^-1 K^-1

mass = 237 mls * 1 g/ml = 237 g

DH_solution = 4.18 J g^-1 K^-1 * 237 g * 35 K = 34,673 J

DH_rxn = -DH_solution = -34,673 J or –34.7 kJ

4. Given the following data:

2C₂H₆(g) + 7O₂(g) -> 4CO₂(g) + 6H₂O(l) DH = -3120 kJ

C(s) + O₂(g) -> CO₂(g) DH = -394 kJ

2H₂(g) + O₂(g) -> 2H₂O(l) DH = -572 kJ

Calculate DH for the reaction:

2C(s) + 3H₂(g) -> C₂H₆(g) (2 points)

2C(s) + 2O₂(g) -> 2CO₂(g) DH = -788 kJ

3H₂(g) + 1½O₂(g) -> 3H₂O(l) DH = -858 kJ

3H₂O(l) + 2CO₂(g) -> C₂H₆(g) + ⁷/₂O₂(g) DH = +1560

2C(s) + 3H₂(g) -> C₂H₆(g) DH = -86 kJ

5. Draw an enthalpy diagram for the reaction in problem #4 where initially carbon, oxygen and hydrogen are converted to carbon dioxide and water. Then, the carbon dioxide and water are converted to ethane gas and oxygen. Show the reaction enthalpy for each reaction, be sure to show the reaction enthalpy for the overall reaction of carbon, oxygen and hydrogen to produce ethane (3 points)



6. Calculate the enthalpy change for the combustion of 1.5 moles of acetylene. Use the Standard Enthalpies of Formation from the chart on page 166 of your book. (2 points)