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**preview**shows page 1. to view the full**5 pages of the document.**CHAPTER 5: GASES

Early Experiments

A. Jan Baptista Van Helmont

a. The first person to attempt the scientific study of “vapors”

b. Described these substances as gas

c. Burned wood and determined the gas, which we now know as CO2, is similar to

air

B. Evangelista Torricelli

a. Performed experiments that showed that air in the atmosphere exerts pressure

b. Designed the first barometer

C. Otto von Guericke

a. Invented an air pump

D. Units of Pressure

a. Most commonly used units are based on the height of the mercury column (in

millimeters) the gas pressure can support in a manometer

b. Millimeters of mercury (mm Hg): (also called torr)

c. Stand atmosphere

i. 1 standard atmosphere=1 atm=760 mm Hg=760 torr

d. Pressure is defined as force per unit area (force/area). Thus, the unit for pressure

in the SI system is the newtons per meter squared (N/m^2) called the pascal (Pa)

i. 1 atm= 101,325 Pa

The Gas Laws of Boyle, Charles, and Avogadro

A. Boyle’s Law

a. PV=k

i. Where k is a constant at a specific temperature for a given sample of air

ii. P is pressure

iii. V is volume

b. There is an inverse relationship between pressure and volume; as pressure drops,

volume goes up

i. V= k/p

1. This is the equation for the straight line y=mx+b where y=V,

x=1/P, m=k, and b=0

c. PV is not quite constant

i. Ideal Gas: A gas that obeys Boyle’s law

d. Used to predict the new volume of a gas when the pressure is changed (at a

constant temperature) or vice versa

B. Charles’s Law

a. Found that volume of a gas at constant pressures increases linearly with the

temperature of the gas.

i. Volumes of all gases extrapolate to 0 at -273.2 degrees C, which is 0

Kelvin

1. Temperature (K)= 0 degrees C + 273

b. Charles’s Law: The volume of each gas is directly proportional to temperature

and extrapolates to zero when the temperature is 0 K

i. Equation: V=bT

1. Where T is temperature and b is proportionality constant

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c. 0 K is absolute zero, and this temperature cannot be attained

C. Avogadro’s Law: equal volumes of gases at the same temperature and pressure contain

the same number of “particles”

a. Equation: V=an

i. Where V is the volume of the gas, n is the number of moles, and a is a

proportionality constant

b. For a gas at constant temperature and pressure, the volume is directly proportional

to the number of moles of gas

The Ideal Gas Law

A. The three laws above can be combined as follows:

a. PV=nRT

i. R is the combined proportionality constant called the universal gas

constant

ii. R= 0.08206 L atm K^-1 mol^-1

B. The ideal gas law is an equation of state for a gas, where the state of the gas is its

condition at a given time

C. Law is an empirical equation based on experimental measurements of the properties of

gases. Gases that obey this equation is said to behave ideally

Gas Stoichiometry

A. Molar volume: volume found using the ideal gas laws equation at standard temperature (0

degrees C) and pressure (1 atm)

a. Oxygen- 22.397

b. Nitrogen- 22.402

c. Hydrogen- 22.433

d. Helium- 22.434

e. Argon- 22.397

f. Carbon Dioxide- 22.260

g. Ammonia- 22.079

B. Molar Mass

a. If the density of a gas at a given temperature and pressure is known, its molar

mass can be calculated

b. See book for equation

i. Moles equals (mass/molar mass)

ii. So P= (m/molar mass)RT/V or m(RT)/V(molar mass)

iii. Density equals m/v so P= d(RT)/molar mass

Dalton’s Law of Partial Pressures

A. For a mixture of gases in a container, the total pressure exerted is the sum of the pressures

that each gas would exert if it were alone.

B. Expressed as Ptotal= P1+P2+P3+…

a. The pressures, P1, P2, and P3 are called partial pressures- each one is the pressure

that gas would exert if it were alone

C. In ideal laws

a. P1= n1RT/V , P2=n2RT/V, etc

b. The total number of moles of particles is the only thing important in ideal gases.

The fact that the pressure exerted by an idea gas is not affected by the identity of

the gas particles reveals two things about ideal gases:

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