# Solving Ideal Gas Law Problems

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number of grams / molar mass = number of moles --For example, if there are 10 g of water, do this: The molecular formula for water is H2O.

The molar mass is then two times the molar mass of H plus the molar mass of O: 2*1.008 15.999 = 18.015 grams per mole If there are 10 grams, to convert that to moles: 10 g ÷ 18.015 g/mol = .5551 moles -UNIVERSAL GAS CONSTANT (R): You want to use this value: 0.0820574587 L · ATM · K-1 · mol-1.

To change °C to K, use the formula T = °C 273T = 127 °C 273 T = 400 KThe second step is to choose the ideal gas constant value of R suitable for our units. Therefore, we should use R = 0.0821 liter·atm/mol·KOur example wants us to find the number of moles of gas.

PV = n RTsolve for nplug in our valuesn = 28.0 mol Answer There are 28.0 moles of argon in the cylinder.

To convert °F to °C, use this method: -first subtract 32 from the °F number -then divide that number by 9 -then multiply that by 5 Don't forget to convert °C to Kelvin afterwards!

--For example, if the temperature is 75 °C, in Kelvin that is: 75 °C 273.15 = 348.15 K Or instead, if the temperature is given as 150 °F, do this: 150 - 32 = 118 118 ÷ 9 = 13.111 13.111 * 5 = 65.556 °C Then to get Kelvin: 65.556 °C 273.15 = 338.706 -Once you've made sure all the units are correct, just plug in to the equation where you isolated the variable you want to find, and solve!The Ideal Gas Law is expressed as PV = n RT where P = Pressure V = Volume n = number of moles of gas particles T = Absolute Temperature in Kelvin and R is the Gas Constant.The Gas Constant, R, while a constant, depends on the units used to measure pressure and volume. R = 0.0821 liter·atm/mol·K R = 8.3145 J/mol·K R = 8.2057 m·atm/mol·K R = 62.3637 L·Torr/mol·K or L·mm Hg/mol·KThis ideal gas law example problem shows the steps needed to use the Ideal Gas Law equation to determine the amount of gas in a system when the pressure, volume, and temperature are known.PRESSURE (P): The unit of pressure must be in units of ATM.The units of pressure can be given in many different units.Also it means the temperature is directly proportional to both the pressure and the volume.The amount of substance is directly proportional to the volume and the pressure. First, you need to figure out what you know from the question, and what you need to find.However, to use the Ideal Gas Law, the best unit to use is called an atmosphere, written "ATM." Here is how to convert from other units of pressure to ATM: 1 ATM = 14.6959488 pounds per square inch (psi) 1 ATM = 29.9246899 inches of mercury (in Hg) 1 ATM = 760 mm mercury (mm Hg) 1 ATM = 760 torr (torr) 1 ATM = 101,325 pascals (Pa) 1 ATM = 101.325 kilopascals (k Pa) 1 ATM = 1.01325 bar (bar) If you see any of these other units of pressure being used, convert them to ATM using the factor given above.--For example, if the problem give the pressure as 30.2 in Hg, do this: 30.2 in Hg ÷ 29.9247 in Hg/ATM = 1.009 ATM -VOLUME (V): The volume must be in units of liters (L).Problem A cylinder of argon gas contains 50.0 L of Ar at 18.4 atm and 127 °C. Solution The first step of any Ideal Gas Law problem is to convert temperatures to the absolute temperature scale, Kelvin.At relatively low temperatures, the 273 degree difference makes a very large difference in calculations.