Mole-mass-volume relationships gases

Because moles are the currency of chemistry, all stoichiometric computations require amounts in moles. In the real world, we measure mass, volume, temperature, and pressure. With the ideal gas equation, our catalog of relationships for mole conversion is complete. Table lists three equations, each of which applies to a particular category of chemical substances. 

Background Avogadro s law (Vin2 = V2ni), where moles, n = mw (grams/mole) exPresses the relationship between molar mass, the actual mass and the number of moles of a gas. The molar volume of a gas at STP, VSTP is equal to the volume of the gas measured at STP divided by the number of moles VSTp = pp. Dalton s Law of Partial Pressure (Ptotai = Pi + P2 + P3 +. ..) and the derivation, Pi = pp Ptotai will also be used in this experiment to predict the volume occupied by one mole of hydrogen gas at STP. 

There are four intrinsic, measurable properties of a gas (or, for that matter, any substance) its pressure P, temperature T, volume (in the case of a gas, the container volume) V, and mass m, or mole number n. The gas density d is a derived quantity, which is m/V. Before the relationships between these properties for a gas are discussed, the units in which they are usually reported will be outlined. 

The relationship between the density p (mass/volume), temperature, and pressure of an ideal gas can be obtained by first relating the specific molar volume, V (volume/mole), to the density. Using a specific set of units for illustration. 

This simply shows that there is a physical relationship between different quantities that one can measure in a gas system, so that gas pressure can be expressed as a function of gas volume, temperature and number of moles, n. In general, some relationships come from the specific properties of a material and some follow from physical laws that are independent of the material (such as the laws of thermodynamics). There are two different kinds of thermodynamic variables intensive variables (those that do not depend on the size and amount of the system, like temperature, pressure, density, electrostatic potential, electric field, magnetic field and molar properties) and extensive variables (those that scale linearly with the size and amount of the system, like mass, volume, number of molecules, internal energy, enthalpy and entropy). Extensive variables are additive whereas intensive variables are not. 

Equation of state (EOS) n. For an ideal gas, if the pressure and temperature are constant, the volume of of the gas depends on the mass, or amount of gas. Then, a single property called the gas density (ratio of mass/volume). If the mass and temperature are held constant, the product of pressure and volume are observed to be nearly constant for a real gas. The product of pressure and volume is exactly for an ideal gas. This relationship between pressure and volume is called Boyle s Law. Finally, if the mass and pressure are held constant, the volume is directly proportional to the temperature for an ideal gas. This relationship is called Charles and Gay-Lussac s law. The gas laws of Boyle and Charles and Gay-Lussac can be combined into a single equation of state PV = nRT, where P is pressure, V volume, Tabsolute temperature, n number of moles and R is the universal gas constant. Ane-rodynamicists us a different form of the equation of state that is specialized of air. Regarding polymers and monomers, equation of state is an equation giving the specific volume (v) of a polymer from the known temperature and pressure and, sometimes, from its morphological form. An early example is the modified Van der Waals form, successfully tested on amorphous and molten polymers. The equation is ... 

Background This experiment uses the concept of continuous variation to determine mass and mole relationships. Continuous variation keeps the total volume of two reactants constant, but varies the ratios in which they combine. The optimum ratio would be the one in which the maximum amount of both reactants of known concentration are consumed and the maximum amount of product(s) is produced. Since the reaction is exothermic, and heat is therefore a product, the ratio of the two reactants that produces the greatest amount of heat is a function of the actual stoichiometric relationship. Other products that could be used to determine actual molar relationships might include color intensity, mass of precipitate formed, amount of gas evolved, and so on. 

The number of moles is a fourth variable that can be added to pressure, volume, and temperature as a way to describe a gas sample. Recall that as the other gas laws were presented, care was taken to state that the relationships hold true for a fixed mass or a given amount of a gas sample. Changing the number of gas particles present will affect at least one of the other three variables. 

In Chapter 3 we used relationships between amounts (in moles) and masses (in grams) of reactants and products to solve stoichiometry problems. When the reactants and/or products are gases, we can also use the relationships between amounts (moles, ri) and volume (V) to solve such problems (Figure 5.12). The following examples show how the gas laws are used in these calculations. 

Relationship between formulas, mass, moles and gas volumes Balanced equations Atomic structure. 

The key relationship is provided by the ideal gas law, which yields the ability to calculate density. To see this, think about n/V as the number of moles per unit volume. This is equal to the (mass) density divided by the molar mass. Replacing n/V with that relationship gives us a gas law in terms of density ... 

This relationship between moles of gas and liters gives you a way to convert the gas from a mass to a volume. For example, suppose that you have 50.0 grams of oxygen gas (O2), and you want to know its volume at STP. You can set up the problem like this (see Chapters 10 and 11 for the nuts and bolts of using moles in chemical equations) ... 

STRATEGIZE Since the reaction occurs under standard temperature and pressure, you can convert directly from the volume (in L) of hydrogen gas to the amount in moles. Then use the stoichiometric relationship from the balanced eqnation to find the number of moles of water formed. Finally, use the molar mass of water to obtain the mass of water formed. 

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