Gaseous State

Chapter 9

9.1 The Behavior of Gases

Characteristics of Gas• Gases consist of Particles that are

relatively far apart• Gas particles move very rapidly• Gas particles have little interaction

until they collide.• Gases expand to fill the available

space.

Description of Gases• Gases can be described in various physical

properties.– Pressure– Temperature– Density– Volume– Number of Particles

• Changing one physical parameter will change one or more others.

Pressure• Pressure (P) = Force/area• There are several units for Pressure.– Pounds/Sq. Inch (psi)– 1 Atmosphere (atm) = 760 mm Hg =

760 torr– 1 atm = 101,325 Pa (pascal)– 1 atm = 14.7 psi

EXAMPLE• Calculate the amount of pressure a 105

lbs. woman exerts by stepping down on a stiletto heel (1/16 sq inch)? Compare this to an Elephant (12,000 lbs., 16 sq. in. foot)?

PROBLEM• The depths of the ocean can exceed

380 atm of pressure. How many pascals is this? How many psi?

9.2 Factors That Affect the Properties of Gases

Boyle’s Law• For a given mass of gas at a constant

temperature, volume varies inversely with pressure.

Implications of Boyle’s Law

Therefore

Ideal Gases• Any gas that behaves according to

the predicted linear relationships.– Pressure/Volume– Volume/Temperature

PROBLEM• Given an ideal gas held at constant mass

and temperature, what would be the volume of the gas if it was originally 125 ml, and its pressure is dropped from 1.40 atm to 0.500 atm?

Charles’s Law• For a given mass of a gas at constant

pressure, volume is directly proportional to temperature on an absolute (Kelvin) scale.

Implications of Charles’s Law

Therefore

Kelvin Scale• So far we have measured

temperature in degrees Celsius, a relative scale.

• Absolute temperature is measure in Kelvin (K, note no degree sign is used), this scale is related to the absolute motion of atoms.

0 K = -273.15 °CTherefore Temp °C +273.15 = Temp K

PROBLEM• Calculate the following temperatures

in Kelvin.

– Boiling Point of Water

– Freezing Point of Water

PROBLEM• Given an ideal gas held at constant mass

and pressure, what would be the temperature of the gas if it was originally at 125 °C, and its volume is dropped from 1.00 L to 0.500 L?

Combined Gas Law• Combining Boyle’s and Charles’s Law

results in the following equation.

PROBLEM• A sample of Hydrogen gas occupies

1.25 L at 80.0 °C and 2.75 atm. What would its volume be at 185 °C and 5.00 atm?

Guy-Lussac and Avagadro• Guy-Lussac’s Law stated that

combined gases always reacted in small whole number ratios (sound familiar?)

• Avagadro hypothesized that the volume occupied by a gas is proportional to the number of gas particles and hence the moles of gas.

Avagadro’s Hypothesis• At a given pressure and temperature,

equal volumes of gas contain equal numbers of moles.

• Standard Temperature and Pressure (STP) are defined as 273.15 K and 1 atm, at which 1.00 mole of gas occupies 22.414 L, defined as molar volume

PROBLEM• What volume would 1.00 mole of gas

occupy at 37°C and 1.00 atm?

9.3 The Ideal Gas Law

Review of the Relationships• Boyle’s Law: (C is a constant)

at constant n, T

• Charles’s Law: at constant n, P

• Avagadro’s Hypothesis: at constant P, T

Combine the Equations• Assume the constants combined

equal another constant we will call the Ideal Gas Constant, R

• Rearrange this into the Ideal Gas Law

So What is the Value for R?• Assuming a standard gas you can

calculate the value of R becomes

For a Standard gas 1.000 mole at 273.15 K and 1.000 atm has a volume of 22.414 L

= 0.08206

PROBLEM• Calculate the Ideal Gas Constant if

pressure is measured in torr

PROBLEMThe volume of an oxygen cylinder is 2.025 L. At a temperature of 32 °C the cylinder has a pressure of 945 torr. How many moles of Oxygen gas are in the cylinder?

PROBLEM• Given the amount of oxygen in the

previous question, what is its mass?

• What is its density?

Partial Pressures• Dalton’s Law of Partial Pressure:

Gases in a mixture behave independently and exert they same pressure as they would alone.

+ +…

PROBLEMGiven a 2.500 L container at 45.00°C, what would be the total pressure in the container from a mixture of 2.100 moles gaseous sulfur dioxide and 1.800 moles hydrogen sulfide?

9.5 Gases and Chemical Reactions

The return of Stoichiometry• You can use the gas laws to solve

stoichiometry problems by converting values between states of matter.

Example• A sample of hydrogen gas has a volume of 8.00 L

at a pressure of 5.00 atm and a temperature of 25 °C. What volume of gaseous water is produced in the following reaction at 150.0 °C and 0.947 atm, if all the hydrogen gas reacts with copper (II) oxide

CuO(s) + H2(g) Cu(s) + H2O(g)ALGORITHM• mol of Hydrogen (PV=nRT)• mol of Water (formula)• V of Water (PV=nRT)

PROBLEMHow many grams of calcium carbonate is formed if 3.45 L of carbon dioxide, measured at 45.0 C and 1.37 atm, react with excess CaO?

CaO(s) + CO2(g) CaCO3(S)