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Chapter 10: Problem 82

You have an evacuated container of fixed volume and known mass and introduce a known mass of a gas sample. Measuring the pressure at constant temperature over time, you are surprised to see it slowly dropping. You measure the mass of the gas-filled container and find that the mass is what it should be-gas plus container-and the mass does not change over time, so you do not have a leak. Suggest an explanation for your observations.

Short Answer

Expert verified
The most plausible explanation for the observed pressure drop over time without a change in total mass is either adsorption of the gas molecules to the container walls or a chemical reaction occurring within the container that forms a product with different properties than the initial gas. Further investigation might help to identify the exact cause behind the pressure drop.

Step by step solution

01

Identifying possible causes for the pressure drop

There could be several reasons for the pressure drop in the container without the total mass changing. To find the correct explanation, we have to consider the possibilities.
02

Check if the gas is undergoing a phase change

When a gas undergoes a phase change (gas to liquid or solid), its pressure will decrease. However, in this case, the temperature is kept constant, so phase change is very unlikely to occur.
03

Check if the gas is adsorbed by the container walls

Adsorption occurs when gas molecules adhere to the surfaces of a solid container. This can cause the observed pressure drop in the container. The mass of the gas would still appear to be constant because the gas molecules are still present, just adhered to the container surface.
04

Check if a chemical reaction is occurring

If a chemical reaction occurs within the container, the pressure might drop due to the products of the reaction having different properties than the initial gas. For instance, if the reaction produces a solid or a liquid, the pressure in the container will decrease. Since the mass in the container does not change, this could be a possible reason for the pressure drop over time.
05

Suggest the most plausible explanation

Based on the analysis, the most plausible explanation for the observed pressure drop over time without a change in total mass is either adsorption of the gas molecules to the container walls or a chemical reaction occurring within the container that forms a product with different properties than the initial gas. Further investigation, such as inspecting the container walls or taking chemical samples from the container, might help to identify the exact cause behind the pressure drop.

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Most popular questions from this chapter

Complete the following table for an ideal gas: $$ \begin{array}{llll} \hline \boldsymbol{P} & \boldsymbol{v} & \boldsymbol{n} & \boldsymbol{T} \\ \hline 2.00 \mathrm{~atm} & 1.00 \mathrm{~L} & 0.500 \mathrm{~mol} & ? \mathrm{~K} \\ 0.300 \mathrm{~atm} & 0.250 \mathrm{~L} & ? \mathrm{~mol} & 27^{\circ} \mathrm{C} \\ 650 \text { torr } & ? \mathrm{~L} & 0.333 \mathrm{~mol} & 350 \mathrm{~K} \\ ? \mathrm{~atm} & 585 \mathrm{~mL} & 0.250 \mathrm{~mol} & 295 \mathrm{~K} \\ \hline \end{array} $$

A quantity of \(\mathrm{N}_{2}\) gas originally held at 5.25 atm pressure in a 1.00-L container at \(26^{\circ} \mathrm{C}\) is transferred to a 12.5-L container at \(20^{\circ} \mathrm{C}\). A quantity of \(\mathrm{O}_{2}\) gas originally at \(5.25 \mathrm{~atm}\) and \(26^{\circ} \mathrm{C}\) in a 5.00-L container is transferred to this same container. What is the total pressure in the new container?

Cyclopropane, a gas used with oxygen as a general anesthetic, is composed of \(85.7 \% \mathrm{C}\) and \(14.3 \% \mathrm{H}\) by mass. \((\mathrm{a})\) If \(1.56 \mathrm{~g}\) of cyclopropane has a volume of \(1.00 \mathrm{~L}\) at 0.984 atm and \(50.0^{\circ} \mathrm{C}\), what is the molecular formula of cyclopropane? (b) Judging from its molecular formula, would you expect cyclopropane to deviate more or less than Ar from ideal-gas behavior at moderately high pressures and room temperature? Explain. (c) Would cyclopropane effuse through a pinhole faster or more slowly than methane, \(\mathrm{CH}_{4} ?\)

At an underwater depth of \(250 \mathrm{ft}\), the pressure is 8.38 atm. What should the mole percent of oxygen be in the diving gas for the partial pressure of oxygen in the mixture to be 0.21 atm, the same as in air at 1 atm?

A gas of unknown molecular mass was allowed to effuse through a small opening under constant-pressure conditions. It required 105 s for \(1.0 \mathrm{~L}\) of the gas to effuse. Under identical experimental conditions it required \(31 \mathrm{~s}\) for \(1.0 \mathrm{~L}\) of \(\mathrm{O}_{2}\) gas to effuse. Calculate the molar mass of the unknown gas. (Remember that the faster the rate of effusion, the shorter the time required for effusion of \(1.0 \mathrm{~L} ;\) that is, rate and time are inversely proportional.)
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