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Exam 6: Gases

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Question 21

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Why does a hot air balloon rise when the air in the balloon is heated?

A) The average kinetic energy of the air molecules increases, and the collisions between these molecules and the walls of the balloon make it rise.
B) The pressure of the gas inside the balloon increases, pushing up on the balloon.
C) The gas expands, forcing some of the gas to escape from the bottom of the balloon, and the decrease in the density of the gas lifts the balloon.
D) The balloon expands, causing it to rise.
E) The hot air rises inside the balloon, which produces enough force to lift the balloon.

F) A) and D)
G) A) and C)

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Question 22

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What is the final temperature in kelvins if a sample of ammonia gas, initially at a pressure of 3.00 atmospheres, a temperature of 500.0 K, and a volume of 275 L is changed to a volume of 200.0 L and a pressure of 2.50 atm?

A) 303 K
B) 436 K
C) 573 K
D) 825 K
E) none of the above

F) A) and E)
G) All of the above

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Question 23

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What volume of NH₃(g) at STP is required to prepare 49.8 g of (NH₄) ₂SO₄ by the reaction of ammonia with sulfuric acid?

Uranium reacts with fluorine to produce a compound that is a gas at 57°C. The density of this gas is 13.0 g/L at 57°C and 1 atm pressure. What is the molecular formula of this compound?

Oxygen is bubbled through water before it is given to a patient in a hospital. What volume of pure oxygen gas at 21.0°C and 750.0 torr pressure would a patient receive if the patient breathed 0.250 L of O₂ bubbled through water at this temperature and pressure? (P_H2O = 19.0 torr at 21°C)

Which of the following gases would diffuse fastest at room temperature?

The root-mean-square speed of CH₄ molecules at 25°C is about 0.56 km/s. What is the root-mean-square speed of a H₂ molecule at 25°C?

Calculate the volume of the flask that would contain 0.40 moles of oxygen, 0.600 moles of nitrogen, and 1.50 moles of hydrogen at 25.0°C and a total pressure of 1.80 atm. Calculate the partial pressure of each gas.

Ether was one of the first anesthetics discovered. Assume that several mL of ether are placed in a bulb with a volume of 293 mL, and the bulb is immersed in water at 36°C until the last drop of liquid disappears, leaving the bulb filled with ether vapor. The bulb is then removed from the water bath, and the weight of ether that condenses in the bulb is measured. If 0.841 grams of ether collect in this experiment at a pressure of 746 mmHg, what is the molecular weight of ether?

Polypropylene is a plastic formed by polymerizing propylene, which has the empirical formula CH₂. If a sample of propylene with a mass of 21.0 grams occupies a volume of 11.2 L at STP (0 °C and 1 atm) , what is the molecular formula of this gas?

Fahrenheit defined 0° as the lowest temperature that could be achieved by adding salt to ice and found that ice by itself freezes at 32° on this scale. Unfortunately, Fahrenheit's measurements were wrong. The lowest temperature that can be achieved by adding salt to ice is -21.2 °C. Calculate the equivalent temperature on the Fahrenheit scale.

0.500 mol of Ar gas occupies a volume of 4.07 L at 25.0 °C and 3.00 atm pressure. What volume will the gas occupy at STP (0.00°C and 1.00 atm pressure) ?

What is the melting point of table salt (NaCl) in degrees Fahrenheit, if salt melts at 801°C?

Which sample would have the largest volume at 25°C and 750 mmHg?

The ideal gas equation predicts that a plot of the pressure times the volume of a gas versus the pressure of this gas should be a horizontal straight line at a fixed temperature. When these quantities are graphed for CO₂, however, we find that PV dips far below the theoretical straight line at first. This can be explained as follows.

Use the Kinetic Molecular Theory to explain on the molecular level the following observations for an ideal gas. I) Decreasing the volume causes an increase in pressure if temperature and number of moles are held constant. II) Increasing the temperature causes an increase in pressure if volume and number of moles are held constant.

Which of the following elements or compounds is most likely to be a gas at room temperature?

Which of the following relationships between the two variables listed for an ideal gas does $\textbf{ not }$ give a straight line graph with a positive slope?

Nitrogen and oxygen are allowed to effuse through a porous barrier at 295 K. If nitrogen effuses at a rate of 0.0355 moles per minute, what is the rate of effusion of oxygen?

Calculate the volume of oxygen at 0°C and 1 atm pressure that can be produced by decomposing 100 mL of hydrogen peroxide if this solution is 27.6% H₂O₂ by weight and the density is 1.09 g/cm³. 2 H₂O₂(l) $\rightarrow$ 2 H₂O(l) + O₂(g)