Lesson 20 Key Question #20 litres of hydrogen gas will be produced by the decomp

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Lesson 20 Key Question #20 litres of hydrogen gas will be produced by the decomposition of 90 L Hoter? (Assume that temperature and pressure are constant,) (2 marks) 2 H20 g) 2 2(g) 02 (g) wa How many grams of oxygen gas must be in a 10.0 L container to exert a pressure of 97.0 kPa at a temperature of 25°C? Show all work (Formal method). (6 marks) Explain why water boils at a lower temperature (« 100°C) in locations such as Denver, Colorado (which is at a fairly high altitude). (3 marks) Use your results from the Lab Activity "Determining the Molar Mass of a Gas" to answer the questions below: 4. a. Create a table summarizing all of the data that you collected for the lab. A T- chart may work best, but you may choose to organize your table in another way. Make sure to include units. (5 marks) b. Calculate the molar mass of the vapour of the volatile liquid. Show all of your work. (6 marks) c. Draw diagrams to compare the particles of the substance in the cup (or Erlenmeyer flask): (i) when it is a liquid; (ii) as it begins to evaporate; and (ii) when the last bit of liquid has just evaporated. (3 marks) d. Why must there be a hole in the foil cap? Why must it be very small? (2 marks) During an operation, the patient is given a mixture of gas containing oxygen (so the patient can breathe) and an anaesthetic gas (so the patient in unconscious). Explain why Dalton's Law of Partial Pressures and the Ideal Gas Law are important with respect to this medical application. (3 marks) 5. 6. A high-pressure natural gas tank is at 3600 psi. The tank contains 4.98 mol of methane (CH4) and 0.66 mol of ethane (C2He). What is the partial pressure (in kPa) of each of the component gases in the tank? Show all work (Formal method). (5 marks)

Explanation / Answer

1.) 1 mole of any gas occupies 22.4L

2H2O 2H2+O2

Converting 90L to moles- 90/22.4 = 4.018 moles

2 moles of water gives 2 moles of hydrogen gas by stoichiometry.

So, 4.018 moles of water will give 4.018 moles of hydrogen gas.

2.) PV = n R T

P is measured in pascals, V is measured in cubic metres, n is measured in moles, and T in kelvins

R has the value 8.314 J/(K·mol)

P = 97 x 103 Pa

V = 10L = 0.01 m3

T= 25 + 273 = 298 K

Substituting all the values in the ideal gas equation

n= 0.3915

Mass of Oxygen= n x 32 (Molar Mass of Oxygen = 32)

Mass of Oxygen= 0.3915 x 32 =12.528 gm

3.)  At higher altitude places such as Denver,Colorado air pressure is lower. There's simply less air pushing down on us the higher we ascend into the atmosphere.

To boil water, you need to apply energy in the form of heat. As energy is transferred to the water molecules, they begin to break the bonds holding them together. The water will boil or turn to vapor as soon as its internal vapor pressure equals the pressure exerted on it by the atmosphere. When that occurs, bubbles begin to form and the water boils.

When atmospheric pressure is lower, such as at a higher altitude, it takes less energy to bring water to the boiling point. Less energy means less heat, which means water will boil at a lower temperature at a higher altitude.

5.)

Dalton’s Law, simply stated, is that the total pressure exerted by a mixture of gases (real or ideal) in a fixed volume is equal to the sum of each gases partial pressure. Recall that the partial pressure of a gas is the pressure exerted by that gas on its container independent of any other gas. Because each gas in a mixture is at the same temperature and is contained in the same volume (i.e. E-cylinder) Dalton’s law states that their individual partial pressures can be simply added to find the total pressure in a container.

For example, consider an E-cylinder containing air at a pressure of 1600psi. Air is a mixture of roughly 21% oxygen and 79% nitrogen by volume. If we apply Dalton’s law we can say the partial pressure of oxygen plus the partial pressure of nitrogen is equal to the total pressure. Therefore, 21% of 1600psi is the partial pressure of oxygen exerted on the cylinder and 79% of 1900psi is the partial pressure of nitrogen exerted on the cylinder.

6.) Moles of methane = 4.98

Moles of ethane = 0.66

Total moles= 4.98+0.66= 5.64

Mole fraction of methane = 4.98 / 5.64 = 0.8829

Mole fraction of ethane = 0.66 / 5.64 = 0.1170

Total pressure (in kpa)= 3600 x 6.89476 = 24821.13 kpa

Partial pressure of methane = Mole fraction of methane x Total pressure = 0.8829 x 24821.13= 21914.57 kpa

Partial pressure of ethane = Mole fraction of ethane x Total pressure = 0.1170 x 24821.13 = 2904.07 kpa

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