## Gases Exam1 and Problem Solutions

**Gases Exam1 and Problem Solutions**

**1.** Which ones of the followings are true according to kinetic theory of gases;

**I.** Speed of gas particles are equal under same temperature.

**II. **Repulsion or attraction forces between gas molecules are too small that they can be neglected

**III.** Increasing temperature increases average kinetic energy of gases.

**Solution:**

**I.** Speed of gas particles is inversely proportional to mass of gas and directly proportional to temperature. Thus, speed of all gas particles are not equal to each other. I is false.

**II.** Since there are large amount of spaces between gas particles, repulsion or attraction force between them is too small and they can be neglected.II is true.

**III.** Average kinetic energies of gases are directly proportional to temperature. III is true.

**2. **System given below is filled with X liquid under 0 ^{0}C and 70 cm Hg atmospheric pressure. If density of X is smaller than Hg and tube has cross section area 1 cm^{2}, find which one of the following statements are true for this system.

**I.** h> 70 cm

**II.** If we use tube having cross section area 2 cm^{2}, h value changes.

**III. **If we put this system in to sea level, h increases.

**Solution:**

**I.** Atmospheric pressure is;

hcm.X=70 cm Hg

H and density of liquid in tube is inversely proportional to each other. So;

d_{X}<d_{Hg} and h>70cm Hg, I is true.

**II.** Cross section are of tube does not affect h value. II is false.

**III.** Atmospheric pressure at sea level is 76 cm Hg, so pressure of system increases and h also increases. III is true.

**3.** Which one of the following conditions make gas behave like ideal gas.

**Solution:**

Gases behave like ideal gas when their temperatures increase and pressures decrease. In given gases, 300^{ 0}C is the highest temperature and smallest pressure is 1 atm. II behaves like ideal gas with respect to other conditions.

**4. **Which ones of the following statements are true related to average molecule speeds of H_{2} and N_{2} gases?

**I.** N_{2}(g) at 40 ^{0}C is slower than H_{2}(g) at 40 ^{0}C

**II.** H_{2}(g) at 80 ^{0}C is slower than N_{2}(g) at 40 ^{0}C

**III.** N_{2}(g) at 80 ^{0}C is faster than N_{2}(g) at 40 ^{0}C

**Solution: **Molar mass of H_{2} is 2 g/mol and molar mass of N_{2} is 28 g/mol.

**I.** At same temperature, molecular speed is inversely proportional to square root of molar masses. Since molar mass of N_{2} is larger than H_{2}, speed of N_{2} molecules are slower than speed of H_{2} molecules. I is true.

**II.** Average molecular speed is directly proportional to square root of temperature. Since temperature of H_{2} is higher than N_{2 }and molar mass of H_{2} is smaller than N_{2}, molecular speed of H_{2} molecules are larger than molecular speed of N_{2} molecules. II is false.

**III.** Since molecular speed is directly proportional to temperature, N_{2 }at 80 ^{0}C has larger molecular speed than N_{2} at 40 ^{0}C. III is true.

**5.** Find value of 0,5 atm in terms of cm Hg.

**Solution:**

We know that there is a relation between atm and cm Hg;

1 atm = 76 cm Hg =760 mm Hg

1 atm is 76 cm Hg

0,5 atm is ? cm Hg

¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

?=38 cm Hg

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