GAS MIXTURES AND PARTIAL PRESSURES

Automobile air bags are inflated by nitrogen gas generated by the rapid decomposition of sodium azide, NaN3i 

Analyze This is a multistep problem. We are given the volume, pressure, and temperature of the N2 gas and the chemical equation for the reaction by which the N2 is generated. We must use this information to calculate the number of grams of NaNj needed to obtain the necessary N2. 

Plan We need to use the gas data (P, V, and T) and the ideal-gas equation to calculate the number of moles of N2 gas that should be formed for the air bag to operate correctly. We can then use the balanced equation to determine the number of moles of NaN3 needed. Finally, we can convert moles of NaN3 to grams. 

Solve The nmnber of moles of N2 is determined using the ideal-gas equation  

We use the coefficients in the balanced equation to calculate the number of moles of NaN3i 

Finally, using the molar mass of NaN3, we convert 

Check The units cancel properly at each step in the calculation, leaving us with the correct units in the answer, g NaN3. 

In the first step in the industrial process for making nitric acid, ammonia reacts with oxygen in the presence of a suitable catalyst to form nitric oxide and water vapor  

Thus far we have considered mainly pure gases— those that consist of only one substance in the gaseous state. How do we deal with mixtures of two or more different gases While studying the properties of air, John Dalton (Section 2.1) made an important observation The total pressure of a mixture of gases equals the sum of the pressures that each would exert if it were present alone. The pressure exerted by a particular component of a mixture of gases is called the partial pressure of that component. Dalton s observation is known as Dalton s law of partial pressures. 

How is the pressure exerted by N2 gas affected when some O2 is introduced into 

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I See the Saunders Interactive General Chemistry CD-ROM, Screen 12.8, Gas Mixtures and Partial Pressures. 

Describe perfect gases, perfect gas mixtures, and partial pressure. How does Henry s law apply to gas solubilities ... 

GAS MIXTURES AND PARTIAL PRESSURES We recognize that in a mixture of gases, each gas exerts a pressure that is part of the total pressure. This partial pressure is the pressure the gas would exert if it were by itself. 

Thus, Oi = yiX. Vapor phases are mostly considered as ideal gas mixtures and partial pressures are used instead of concentrations. They are defined in the same manner as in Eq. (2.140), the mole numbers, however, are replaced by the respective... 

Before calculating the pressures, we must visualize the reaction vessel. The container s total volume is 5.00 L, but 0.150 L is occupied by the aqueous solution. This leaves 4.85 L for the gas mixture. The partial pressure of hydrogen is calculated using the ideal gas equation and assuming that no H2 remains in solution this is a good assumption because hydrogen gas is not very soluble in water ... 

In a gas mixture, the partial pressure of H2 is 200 torr, that of C02 is 150 torr, and that of CH4 is 320 torr. What is the total pressure What are the mole fractions of the three components ... 

The volume ratios that correspond to mole ratios involve volumes of separate gas samples at the same temperature and pressure. In gas mixtures, the partial pressure ratios are equal to the mole ratios. 

Thus, for the ideal gas mixture, the partial pressure of species i is equal to the pressure that would be exerted if the same number of moles of that species. N alone were contained in the same volume V and maintained at the same temperature T as the... 

Equation 9.3.3 is the ideal gas equation with the partial pressure of a constituent substance replacing the total pressure, and the amount of the substance replacing the total amount. The equation shows that the partial pressure of a substance in an ideal gas mixture is the pressure the substance by itself, with all others removed from the system, would have at the same T and V as the mixture. Note that this statement is only true for an ideal gas mixture. The partial pressure of a substance in a real gas mixture is in general different from the pressure of the pure substance at the same T and V, because the intermolecular interactions are different. 

In a gas mixture the partial pressure of methane is 154 torr of ethane, 178 torr and of propane, 449 torr. Find the total pressure exerted by the mixture. 

A furnace has a spherical cavity of 0.5-m diameter. Contents are a gas mixture (CO2 partial pressure of 0.25 atm N2 partial pressure of 0.75 atm) at a total pressure of 1 atm and 1400 K. What cooling rate is needed to maintain the cavity wall (blackbody) at 500°K ... 

The rate is therefore assumed constant using the average partial pressures for CH4 and CS2. For an ideal gas mixture, the partial pressure of component i is ... 

The simulation was made nnder the following conditions. Either pnre CH gas, or pure C2Hg gas or equimolar mixture of CH and C2Hg was considered for the simnla-tion. Temperature was 300 K and pressure in H region was 0.5 MPa for pnre gas. For the gas mixture the partial pressure of each component was set equal to 0.5 MPa. 

Here ig is the limiting current for the reacting species, i.e., O2 for the cathode, with n = 4, and H2 or CO for the anode, with n = 2 [9]. The limiting current of a species depends on its diffusivity in the surrounding gas mixture, its partial pressure, and the porosity, tortuosity, and thickness of the electrode. For H2 fuel, the limiting current density can be calculated [15] as ... 

When Che diameter of the Cube is small compared with molecular mean free path lengths in che gas mixture at Che pressure and temperature of interest, molecule-wall collisions are much more frequent Chan molecule-molecule collisions, and the partial pressure gradient of each species is entirely determined by momentum transfer to Che wall by mechanism (i). As shown by Knudsen [3] it is not difficult to estimate the rate of momentum transfer in this case, and hence deduce the flux relations. 

Assuming an ideal gas mixture at amiospheric pressure, calculate llie mole fraction and ppm of a component if its partial pressure is 19 mniHg. 

The total fixed volume of a mixture of gases and vapors at a giv en condition is the same as the olume of any one component (gas laws), and its pressure is composed of the sum of the individual partial pressures of each component. 

The desorption using a nonadsorbing medium such as nitrogen equals a pressure swing process because the purge gas reduces the partial pressure of the n-alkane and works as a vacuum. This variant also is only suitable for the isolation of n-alkanes from low molecular weight hydrocarbon mixtures like gasoline fractions. 

The partial pressure is defined as the pressure each gas would exert if it alone were to occupy the entire volume occupied by the mixture at the same temperature. Thus, the total pressure exerted by A and B is equal to the sum of the partial pressure of A, PA, and partial pressure of B, PB... 

Gases mix. Gases mix better than liquids do and infinitely better than solids. So what s the relationship between the total pressure of a gaseous mixture and the pressure contributions of the individual gases Here s a satisfyingly simple answer Each individual gas within the mixture contributes a pcirtial pressure, and adding the pcirtial pressures yields the total pressure. This relationship is summcirized by Dalton s law of partial pressures for a mixture of individual gases ... 

What is responsible for the pressure in a gas mixture Because the pressure of a pure gas at constant temperature and volume is proportional to its amount (P = nRT/V), the pressure contribution from each individual gas in a mixture is also proportional to its amount in the mixture. In other words, the total pressure exerted by a mixture of gases in a container at constant V and T equals the sum of the pressures of each individual gas in the container, a statement known as Dalton s law of partial pressures. 

These two equations are applicable to mixtures of ideal gases as well as to pure gases, provided n is taken to be the total number of moles of gas. However, we must consider how the properties of the gas mixture depend upon the composition of the gas mixture and upon the properties of the pure gases. In particular, we must define the Dalton s pressures, the partial pressures, and the Amagat volumes. Dalton s law states that each individual gas in a mixture of ideal gases at a given temperature and volume acts as if it were alone in the same volume and at the same temperature. Thus, from Equation (7.1) we have... 

Dalton s law states that the sum of the pressures of the gases in a mixture is the total pressure exerted—the volume and temperature are constant (Ptotai = P + Pi + P3 + ). The pressure of each gas is the partial pressure of that gas. As with the other gas laws, this law only holds true when working with ideal gases however, this law may be applied to the problems in this book for predicting results. 

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