CHY 103 Lecture 5: CH9-2.pdf

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10 May 2015

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The ideal-gas law is a wonderful relationship because it is composed of three other laws (boyle"s, This allows the flexibility to tailor the ideal-gas law to suit our needs. Suppose we have a metal cylinder that holds 50. 0 l of oxygen at 18. 5 atm and 21ec. The above question is a common one for gases, a before-and-after scenario. A 0. 50 mol sample of oxygen gas is confined at 0ec in a cylinder with a moving piston. The gas has an initial pressure of 1. 0 atm. The gas is then compressed by the piston so that its final volume is half the initial volume. The final pressure of the gas is 2. 2 atm. In general, whenever you have a gas under two sets of conditions there will at least be one constant, i. e. , r never changes for the gas. Using this we can make the following general relationship:

Related Questions

Â± Changes in Volume

The ideal gas law (PV=nRT) describes the relationship among pressure P, volume V, temperature T, and molar amount n. When some of these variables are constant, the ideal gas law can be rearranged in different ways to take the following forms where k is a constant:

Name	Expression	Constant
Boyle's law	PV=nRT=k	n and T
Charles's law	VT=nRP=k	n and P
Avogadro's law	Vn=RTP=k	T and P

Part A

A certain amount of chlorine gas was placed inside a cylinder with a movable piston at one end. The initial volume was 3.00 L and the initial pressure of chlorine was 1.15 atm . The piston was pushed down to change the volume to 1.00 L. Calculate the final pressure of the gas if the temperature and number of moles of chlorine remain constant.. (Figure 1)

Express your answer with the appropriate units.

Pfinal =

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Part B

In an air-conditioned room at 19.0 âC, a spherical balloon had the diameter of 50.0 cm. When taken outside on a hot summer day, the balloon expanded to 51.0 cm in diameter. What was the temperature outside in degrees Celsius? Assume that the balloon is a perfect sphere and that the pressure and number of moles of air molecules remains the same.

Express your answer with the appropriate units.

outside temperature =

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Part C

A cylinder with a movable piston contains 2.00 g of helium, He, at room temperature. More helium was added to the cylinder and the volume was adjusted so that the gas pressure remained the same. How many grams of helium were added to the cylinder if the volume was changed from 2.00 L to 4.10 L ? (The temperature was held constant.)

Express your answer with the appropriate units.

mass of helium added =

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A number of empirical relationships or laws exist among the parameters used to describe the behavior of gases (for example, Avogadro's law and the relation of molecular velocity to temperature from kinetic molecular theory). Some of these laws relate initial and final conditions of two changing parameters while all other parameters are held constant (for example, Boyle's law for pressure-volume relationships). Other relationships, such as the ideal gas law, relate parameters without need for initial and final conditions. Classify each situation by the equation that would quantify it. A container of ammonia cleaner is stored in the janitor's closet off a lecture hall after being used at night for cleaning. The container has a very small hole in the lid. The next morning the entire lecture hall smells of ammonia. How would you calculate the speed of the ammonia molecules as they move out into the lecture hall? The pressure on a tire pump is read. The handle of the pump is pushed down as far as possible. The reading of the pressure on the gauge is taken again. How would you calculate the final pressure? The burner under a hot air balloon is ignited and the balloon expands. How would you calculate the expanded volume of the balloon? A front-end collision causes the air bag in an automobile to deploy by the reaction of sodium azide to produce nitrogen gas. How would you calculate how much sodium azide is needed to fill a standard size bag with nitrogen under STP conditions? Aerosol cans have a label that warns the user not to use them above a certain temperature and not to dispose of them by incineration. Even an empty can contains residual gaseous propellant. If the residual pressure in the can is 1.31 atm when it is sitting on a shelf near a furnace, how could you calculate the pressure when the can is placed on top of the furnace where the temperature reaches the boiling point of water? In an automobile engine, at the end of the upstroke the piston is at its maximum height in a cylinder of exact dimensions. At this time, a precisely measured mixture of fuel and oxidant ignites to form gaseous products. If the ignition temperature is known, how could you calculate the pressure inside the cylinder just before the piston moves downward? Drag the appropriate items to their respective bins.

M 121 1 201 Ideal Gas Law (PV n Experiment to T ) Determine the Ideal Gas Constant R 1. Conduct basic measurements, measurement , mathematical calculations and conversions for of volume, pressure, and temperature: calculate percent error and account for sources of error in an e xperimental result name and by following safety proced ty experiments for a redox reaction by using equipment identifiable by form chemical calculations using mass, mole and volumes and idenify limitatios of measuring devices in order to state the uncertainty/significant figures in measurements and calculation results. 5. Demonstrate a proficiency in relating the chemistry of gases to everyday phenomenon. Introduction Molecules in gases have very little attraction for one another, because relative to their size, they are so far apart from each other. For this reason we can often assume that a gas behaves "idcally." meaning that the physical behavior of the gas is independent of the composition of the gas. If a gas behaves ideally, then its physical properties can be described by the Ideal Gas Equation: Let's consider why the variables in the ideal gas equation have the relationships expressed in Equation 1aã The ideal gas equation assumes that there are no attractive forces between gas molecules. One can picture two billiard balls bouncing off one another in a totally clastic collision. If these molecules are placed in a balloon the collisions will occur not only with each other but also with the wall of the balloon, causing the balloon to expand. This expansion can be measured as a volume (V). More molecules will cause more collisions and thus more expansion. Therefore the quantity of molecules or number of moles (n) is directly proportional to the volume, and thus volume and number of moles appear on opposite sides of the equation. Another factor to consider is the kinetic energy of these molecules. Kinetic energy is related to the temperature (T) of the molecules, in that the kinetic energy. If the collisions with the wall of the balloon are happening at a very high speed due to high kinetic energy, the collisions will be harder and more frequent and thus the wall of the balloon will be pushed out further (a larger volume) than if the kinetic energy were less. The result is that volume is also directly proportional to the temperature. This relationship is seen in Equation la with (T) on the right side of the equation and (V) on the left. higher the temperature the greater the considered. While the molecules inside the balloon are pushing the balloon out, there are also molecules in thea Finally the pressure of the outside environment (atmospheric pressure) needs to be 59

CHY 103 Lecture 5: CH9-2.pdf

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