GASESGASES(Part 3)(Part 3)

Gas Laws

A Quick Review Of What We’ve Learned

Boyle’s LawBoyle’s LawP P αα 1/V 1/VThis means Pressure This means Pressure

and Volume are and Volume are INVERSELY INVERSELY PROPORTIONAL PROPORTIONAL if if moles and moles and temperature are temperature are constant. For constant. For example, P goes up example, P goes up as V goes down.as V goes down.

PP11VV11 = P = P22 V V22

Robert Boyle (1627-1691). Son of Earl of Cork, Ireland..

Nice lipstick, dude!

Charles’s Charles’s LawLaw

If n and P are If n and P are constant, constant, then V then V αα T T

V and T are directly V and T are directly proportional.proportional.

VV11 V V22

==

TT11 T T22

• If one temperature If one temperature

goes up, the goes up, the volume goes up!volume goes up!

Jacques Charles (1746-Jacques Charles (1746-1823). Isolated boron and 1823). Isolated boron and studied gases. Balloonist.studied gases. Balloonist.

Somebody’s got a case of the Mondays

Gay-Lussac’s LawGay-Lussac’s Law

If n and V are constant,

then P α TP and T are directly

proportional.P1 P2

=

T1 T2

• If one temperature goes up, the pressure goes up!

Joseph Louis Gay-Joseph Louis Gay-Lussac (1778-1850)Lussac (1778-1850)

Balloons make me Happy!

Combined Gas Law

If you should only need one of the other gas laws, you can cover up the item that is constant and you will get that gas law!

Boyle’s Law

Charles’ Law

Gay-Lussac’s Law

=P1 V1

T1

P2 V2

T2

IDEAL GAS LAWIDEAL GAS LAW

Brings together gas properties.

BE SURE YOU KNOW THIS EQUATION!

P V = n R TP V = n R T

Gases in the AirThe % of gases in air Partial pressure (STP)

78.08% N2 593.4 mm Hg

20.95% O2 159.2 mm Hg

0.94% Ar 7.1 mm Hg

0.03% CO2 0.2 mm Hg

PAIR = PN + PO + PAr + PCO = 760 mm Hg 2 2 2

Total Pressure 760 mm Hg

Dalton’s Law of Partial Dalton’s Law of Partial PressuresPressures

What is the total pressure in the flask?What is the total pressure in the flask?

PPtotaltotal in gas mixture = P in gas mixture = PAA + P + PBB + ... + ...Therefore, Therefore, PPtotaltotal = P = PHH22OO + P + POO22

= 0.48 atm = 0.48 atm

Dalton’s Law: total P is sum of Dalton’s Law: total P is sum of PARTIALPARTIAL pressures. pressures.

2 H2 H22OO2 2 (l) ---> 2 H(l) ---> 2 H22O (g) + OO (g) + O2 2 (g)(g)

0.32 atm 0.32 atm 0.16 atm 0.16 atm

Dalton’s Dalton’s LawLaw

John DaltonJohn Dalton1766-18441766-1844

Gases and StoichiometryGases and Stoichiometry

2 H2O2 (l) ---> 2 H2O (g) + O2 (g)

Decompose 1.1 g of H2O2 in a flask with a volume of 2.50 L. What is the volume of O2 at STP?

Solve a gas law stoichiometry problem just like any other stoichiometry problem…the unit you want to go to goes on top…the unit you want to get rid of goes on bottom.

Gases and Gases and StoichiometryStoichiometry

2 H2 H22OO2 2 (l) ---> 2 H(l) ---> 2 H22O (g) + OO (g) + O2 2 (g)(g)

Decompose 1.1 g of HDecompose 1.1 g of H22OO22 in a flask with a volume of 2.50 L. What is the in a flask with a volume of 2.50 L. What is the volume of Ovolume of O22 at STP? at STP?

SolutionSolution1.1 g1.1 g HH22OO22 1 mol H 1 mol H22OO22 1 mol O 1 mol O22 22.4 L O 22.4 L O22

34 g H34 g H22OO22 2 mol H 2 mol H22OO22 1 mol O 1 mol O22

= 0.36 L O2 at STP

Gas Stoichiometry: Practice!

A. What is the volume at STP of 4.00 g of CH4?

4.00 g CH4 x 1 mole CH4 x 22.4 L = 5.58 L

16.05g CH4 1 mole

B. How many grams of He are present in 8.0 L of gas at STP?

8.0 L He x 1 mole x 4.00g He = 1.4 g He

22.4 L 1 mole He

Gases and Stoichiometry Gases and Stoichiometry (cont.)(cont.)

• If the problem IS NOT IS NOT at STPSTP…1.Do an A to B stoichiometry problem solving

for moles of the “B” compound2.Use PV = nRT to solve for the variable