GASES AND THEIR BEHAVIOR

Chapter 5

Properties of Gases

• Only 4 quantities are needed to define the state of a gas:

• 1). The quantity of the gas, n (in moles)

• 2). The temperature of the gas, T (Kelvin)

• 3). The volume of a gas , V (Liters) 1000mL=1L

• 4). The pressure of the gas, P (atmospheres)

Gas Pressure

• A measure of the force that it exerts on its container. Force is the physical quantity that interferes with inertia. Gravity is the force responsible for weight.

• Force = Mass x acceleration, Newton’s 2nd law.

• N = kg x m/s2

• Pressure – Force/unit area; N/m2

• Barometer – invented by Evangelista Torricelli in 1643. Uses the height of a column of mercury to measure gas pressure (especially atmospheric)

• 1mmHg = 1torr

• 760mmHg = 760torr = 1atm = 101.325kPa

• 101.325kPa = 14.7psi (pounds per square inch)

Practice problems

• 515mmHg in kPa

727mmHg into kPa

52.5kPa into atm

Your problems

• 1. 52.5kPa into atm• 2. 0.729atm into mmHg• 3. 522torr into kPa• 4. 1.10atm into psi• 5. 800mmHg into atm• 6. 125kPa into torr• 7. Rank the following pressures in decreasing

order of magnitude (largest first, smallest last): 75kPa, 300torr, 0.60atm and 350mmHg

Gas Laws: The experimental basis

• Boyle’s law: The father of chemistry. • His law states the volume of a confined gas is

inversely proportional to the pressure exerted on the gas.

• Pressure and volume are inversely proportional• Temperature is constant• For a given quantity of a gas at constant

temperature, the product of pressure and volume is a constant.

• P1V1 = P2V2

Example

• A Sample of carbon dioxide with a pressure of 55mmHg and a volume of 125mL is placed in a new flask. The pressure of the gas in the new flask is 78mmHg. What is the volume of the new flask?

Charles law

• If a given quantity of gas is held at a constant pressure, then its volume is directly proportional to the Absolute temperature. Must use Kelvin

• V1T2=V2T1

Avogadro’s Law

• Avogadro’s law says that for a gas at constant temperature and pressure , the volume is directly proportional to the number of moles of gas.

• V1n2=V2n1

• V1= Initial volume• n1 = initial number of moles• V2= final volume• n2= final number of moles

• A 5.20L sample at 18C and 2.00 atm pressure contains 0.436 moles of a gas. If we add an additional 1.27moles of the gas at the same temperature and pressure, what will the total volume occupied by the gas be.

• Suppose we have a 12.2L sample containing 0.50mol oxygen gas(O2) at a pressure of 1atm and a temperature of 25C. If all this 02 were converted to ozone at the same temperature and pressure, what would be the volume of the ozone?

• Charles’s Law

• 1) If I have 45 liters of helium in a balloon at 250 C and increase the temperature of the balloon to 550 C, what will the new volume of the balloon be?

•

• 3) I have 130 liters of gas in a piston at a temperature of 2500 C. If I cool the gas until the volume decreases to 85 liters, what will temperature of the gas be?

• 2) Calcium carbonate decomposes at 12000 C to form carbon dioxide and calcium oxide. If 25 liters of carbon dioxide are collected at 12000 C, what will the volume of this gas be after it cools to 250 C?