Chemistry 121 Oregon State University Worksheet 9 Dr. Richard L nafshun




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Chemistry 121 Oregon State University

Worksheet 9 Dr. Richard L Nafshun
1. What is the root-mean-square speed of H2 (use a molar mass of 2.0 g/mol or 0.0020 kg/mol) at 296 K and 1.00 atm (around room temperature and pressure)?
What is the root-mean-square speed of He (use a molar mass of 4.0 g/mol or 0.0040 kg/mol) at 296 K and 1.00 atm (around room temperature and pressure)?
Which gas is traveling faster? Why?
The mass you used for He was twice as great as that used for H2. Is He traveling twice as slow as H2? Why?
2. Consider the following six gases: CO (g) CO2 (g) Xe (g) He (g) F2 (g) SF6 (g)

Of these, which gas molecule has the greatest velocity at room temperature? Explain.

Of these, which gas molecule has the lowest velocity at room temperature? Explain.
3. What is the mass of a 3.000 liter balloon that contains SF6 (g) at 1.01 atm and 296.0 K?

4. Consider a sealed balloon containing nitrogen gas. Which of the following is false? Why?

(A) When the temperature is decreased, the velocity of the gas molecules decreases.

(B) When the temperature is decreased, the volume of the balloon decreases.

(C) When the temperature is decreased, the moles of gas inside the balloon decrease.

(D) When the temperature is decreased, the pressure inside the balloon stays constant.

(E) A 22.4-L balloon, at 1.00 atm, and 273.15 K contains one mole of nitrogen gas.
5. A student burns 30.00 grams of hydrogen gas (H2) in oxygen to produce steam at 1.05 atm and 296 K. How many liters of steam are produced?
6. Identify the following processes as endothermic or exothermic. Explain. Write out each change as a balanced chemical reaction, including phases (see first example).

(A) water boils

Endothermic. Heat is supplied to system. H20 (l)  H2O (g)

(B) ice melts


(C) steam condenses
(D) water freezes
(E) alcohol boils
(F) combustion of methane (CH4) with diatomic oxygen
(G) dissolution of ammonium nitrate in water (as demonstrated in lecture)
(H) detonation of dynamite
(I) metabolism of glucose
7. For each system below, give the signs (positive or negative) for w, q, and E:

(A) A system does 10 kJ of work and gives off 220 kJ of heat.


(B) A system does 50 kJ of work and absorbs 65 kJ of heat.
(C) A system does 10 kJ of work and gives off 220 kJ of heat.
(D) A system has 120 kJ of work done on it and gives off 50 kJ of heat.
(E) A system has 70 kJ of work and gives off 85 kJ of heat.
(F) A system does 75 kJ of work and gives off 75 kJ of heat.
(G) A system cools down while expanding.
(H) A system heats up a little while expanding a lot.
(I) A endothermic reaction does not expand.

Substance

J/gּ˚C




Substance

J/gּ˚C


Water

4.186




Soil (typical)

1.046

Methyl Alcohol

2.549




Air

1.046

Ice

2.093




Aluminum

0.9

Steam

2.009




Mercury

0.138

Benzene

1.75




Gold

0.13

Wood (typical)

1.674




Lead

0.128


8. A student obtains 5400 grams of water (approximately 6 quarts) at 23.0 ˚C. Calculate the heat required to increase the temperature of the water to 100.0 ˚C.
9. A student obtains 5400 grams of water at 100.0 ˚C. Calculate the heat released when temperature of the water decreases to 23.0 ˚C.
If a 10,000 gram sample of gold absorbed all of this heat released from the water, what would be the change in temperature of the gold sample?
10. Steam comes in contact with your arm. What is the sensation? Why?
11. The heat of formation of urea, CO(NH2)2 (s) is –333.19 kJ/mol. Write the chemical equation associated with this reaction (include phases—s, l, g, or aq).
12. (A Table will be helpful) How much energy is given off when 8.00 moles of

CO (g) is formed from the elements (at 25 ˚C and 1 atm).


How much energy is given off when 500.0 g CO (g) is formed from the elements (at 25 ˚C and 1 atm).
13. Consider:

2 C8H18 (l) + 25 O2 (g) → 16 CO2 (g) + 18 H2O (l) ΔH˚reaction = -10900 kJ

How much energy is released when one mole of octane, C8H18, is combusted?

What is ΔH˚ when 9 moles of water are formed?


14. (Table 6.2 will be helpful) Calculate ΔH˚ for the following reaction:

CH4 (g) + 2 O2 (g) → CO2 (g) + 2 H2O (l) ΔH˚reaction = ?


15. (Table 6.2 will be helpful) Calculate ΔH˚ for the following reaction:

C2H2 (g) + 5/2 O2 (g) → 2 CO2 (g) + H2O (l) ΔH˚reaction = ?


16. The heat of formation of NH4Cl (s) is –315.4 kJ/mol. Write the chemical equation associated with this reaction (include phases—s, l, g, or aq).

17. From the following heats of reaction


2 SO2(g) + O2(g)  2 SO3(g) H = – 196 kJ (1)

2 S(s) + 3 O2(g)  2 SO3(g) H = – 790 kJ (2)

calculate the heat of reaction for

S(s) + O2(g)  SO2(g) H = ? kJ (3)


18. Calculate the standard reaction enthalpy for the photosynthesis reaction,

6 CO2(g) + 6 H2O(l)  C6H12O6(s) + 6 O2(g) = ? kJ

The heat of formation of glucose, C6H12O6(s), is – 1274.5 kJ/mol; other values are listed in the text.
19. Given the following reactions and their enthalpy changes, calculate the enthalpy change for

2 NO2(g) ----> N2O4(g)



Equations

Change in Heat Energy

N2(g) + 2 O2(g) ---> 2 NO2(g)

67.8 kJ

N2(g) + 2 O2(g) ---> N2O4(g)

9.67 kJ


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