Section 2

Avogadro’s Law (5.2)

Ideal Gas Law (5.3)

Gas Stoichiometry (5.4)

Chemistry- Unit 7

• volumes of gas at the same temperature

and pressure contain equal number of

molecules

Volume & Amount

Avogadro’s Law

k is a constant for that specific gas

V = kn

Volume & Amount

Avogadro’s Law

• For 1 mole of an ideal gas at 0°C and 1 atm,

the volume of the gas is 22.42 L.

• 1 mol gas = 22.4 L gas (@ STP)

• STP = standard temperature and pressure

0°C and 1 atm

Therefore, the molar volume is 22.42 L at STP.

If 2.45 mol of argon gas occupies a volume

of 89.0 L, what volume will 2.10 mol of

argon occupy under the same conditions of

temperature and pressure?

76.3 L

Concept Check

• mathematical relationship between

pressure, volume, temperature and

amount of a gas

• We can bring all of these laws together

into one comprehensive law:

Ideal Gas Law

PV= k

T

V = knPV

≈ knT

R = 0.0821 L·atm/mol·K (the universal gas constant)

Ideal Gas Law

PV≈ kn

T

PV= Rn

TPV = nRT

Ideal Gas Law

• For 1 mole of an ideal gas at 0°C and 1

atm, the volume of the gas is 22.42 L.

• STP = standard temperature and pressure

0°C and 1 atm

Therefore, the molar volume is 22.42 L

at STP.

Molar Volume of an Ideal Gas

An automobile tire at 23.0°C with an internal

volume of 25.0 L is filled with air to a total

pressure of 3.18 atm. Determine the

number of moles of air in the tire.

3.27 mol

Concept Check

What is the pressure in a 304.0 L tank that

contains 5.670 kg of helium at 25.00°C?

114 atm

Concept Check

At what temperature (in °C) does 121 mL of

CO2 at 27°C and 1.05 atm occupy a volume

of 293 mL at a pressure of 1.40 atm?

696°C

Concept Check

A sample of oxygen gas has a volume of

2.50 L at STP. How many grams of O2 are

present?

3.57 g

Concept Check

Consider the following reaction:

4Al(s) + 3O2(g) → 2Al2O3(s)

It takes 2.00L pure oxygen gas at STP to

react completely with a certain sample of

aluminum. What is the mass of aluminum

reacted?

3.21 g Al

Concept Check

Ideal Gas Law Summary

PV = nRT

PV = nRT P1V1 = P2V2

PV = nRT

V nR=

T P

V1 V2

= T1 T2

If temp and amount stay constant…

If P and n stay constant…

Rearrange for V & T

Ideal Gas Law

Boyle’s Law

Charles’ Law

Ideal Gas Law Summary

PV = nRT

PV = nRT

PV = nRT

P nR=

T V

P1 P2

= T1 T2

PV= nR

T

P1V1 P2V2

= T1 T2

If V and n stay constant…Rearrange for P & T

Rearrange for P, V & T

If n stays constant…

Ideal Gas Law

Gay-Lussac’s Law

Combined Gas Law

Ideal Gas Law Summary

PV = nRT

P1 P2

= T1 T2

P1V1 P2V2

= T1 T2

By knowing the Ideal Gas Law, you can

determine all other equations needed.

V1 V2

= T1 T2

P1V1 = P2V2

A sample of methane gas (CH4) having a

volume of 2.80L at 25oC and 1.65atm was

mixed with a sample of oxygen gas having

a volume of 35.0L at 31oC and 1.25atm.

The mixture was then ignited to form carbon

dioxide and water. Calculate the volume of

CO2 formed at a pressure of 2.50atm and a

temperature of 125oC.

2.47 L

Concept Check

Molar Mass of a Gas

• Molar mass (M)

• grams per molem

M =n

mn =

MRearrange for n

PV = nRT ormRT

PV = M

mRTM =

PVSubstitute for n Rearrange for M

(if needed)

At 18oC and 765torr, 2290mL of a gas

weighs 3.71grams. Calculate the molecular

mass of the gas?

38.3 g/mol

Concept Check

Density of a Gas

• Mass per volume

mD =

V

Starting with the equation for Molar Mass

mRTM =

PV

DRTM =

P

MPD =

RTSubstitute for m/V Rearrange for D

(if needed)

What is the density of F2 at STP (in g/L)?

1.70 g/L

Concept Check

The volume of a quantity of sulfur dioxide at

18oC and 1500torr is 4.3L. Calculate its

volume at STP?

8.0L

Concept Check

If a gas occupies 3.00L at STP, what

volume will it occupy at 300oC and 25atm?

0.25L

Concept Check

Calcium metal reacts with hydrochloric acid

to yield hydrogen and calcium chloride.

Determine the volume of hydrogen gas at

1.00atm and 18oC produced from the

reaction of 12.2g of calcium with excess

hydrochloric acid.

7.27L H2

Concept Check

A volume of 95cm3 of nitrous oxide at 27oC

is collected over mercury in a graduated

tube, the level of mercury inside the tube

being 40mm above the outside mercury

level when the barometer reads 750torr.

Compute the volume of the same mass of

gas at STP.

.81L = 810mL

Concept Check

Recommendations

• List out the variables.

– Convert all variables that need conversion.

• Ask: It is “a before and after” or is it

“a snapshot.”

• Start with Ideal Gas Law then convert to

needed equation.

• Solve.

Gas Laws Review

Section 2Homework Set

Chemistry- Unit 7

pg 225 #43, 44, 45, 46, 49, 50,

65, 66, 71, 75, 77