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Final Grade for CHE 103. Calculated as stated in syllabus: EXAM1 + EXAM2 + EXAM 3 + QUIZZES 350. Outline. I. Gases & Gas Laws - Kinetic Molecular Theory - Simple variable relationships - Ideal/Combined Gas Law. - PowerPoint PPT Presentation
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Final Grade for CHE 103
Calculated as stated in syllabus:
EXAM1 + EXAM2 + EXAM 3 + QUIZZES 350
Outline
I. Gases & Gas Laws- Kinetic Molecular Theory- Simple variable relationships
- Ideal/Combined Gas Law
States of Matter - solid, liquid, gas
Gaseous State
Characterized by dominance of kinetic energy over potential energy Gas particles have enough kinetic energy to move
far apart from each other. There is very little attraction between particles
Four Important Gas Variables
1. n = number of moles 2. T = temperature; must be in Kelvin!
K = oC + 273.15 3. V = Volume 4. P = Pressure = force/area
1 atm = 760 mm Hg
Relationship Between Pressure and Volume (Boyle’s Law) When the pressure is increased on a gas, its volume goes down.
PV = constant (T fixed)
useful form: P1V1 = P2V2
Volume/Pressure Calculation A balloon is inflated to a volume of 12.6L on a day when the
atmospheric pressure is 675 mm Hg. The next day, a storm drops the pressure to 651 mm Hg. Assuming constant temperature, what is the new volume of the balloon?
Relationship Between Temperature and Volume (Charles’ Law) When the temperature (K) is increased on a gas, its volume
goes up by a constant: V/T = constant (P fixed)
useful form: V1/T1 = V2/T2
Volume/Temperature Calculation The volume of a sample of air at 30. oC is 3.50 L. Assume that
the pressure is held constant. What would be the volume of air at 300. oC?
Relationship between Temperature and Pressure (Gay-Lussac’s Law) When the temperature (K) is increased on a gas, its pressure
goes up as a constant: P/T = constant (V fixed)
Useful form: P1/T1 = P2/T2
When the Temperature increases, gas molecules are moving faster and hitting the sides of their container more….creating more pressure….according to KMT!
Pressure/Temperature Calculations Consider a container with a volume of 22.4 L filled with a gas at
1.00 atm at 273 K. What will be the new pressure if the temperature increases to 298 K?
P1/T1 = P2/T2
P1 = 1.00atm, T1 = 273KP2 = ? T2 = 298K
P2 = (1.00atm)(298K) = 1.09atm (273K)
Avogadro’s Law: Volume and MolesIn Avogadro’s Law: The volume of a gas is
directly related to the number of moles of gas
T and P are constant V1 = V2 n1 n2
Learning Check
If 0.75 mol of helium gas occupies a volume of 1.5 L, what volume will 1.2 mol of helium occupy at the same temperature and pressure?1) 0.94 L2) 1.8 L3) 2.4 L
V2 = (1.5L)(1.2mol)
(0.75mol)
The volumes of gases can be compared when they have the same conditions of temperature and pressure (STP, Standard Temperature and Pressure).
Standard temperature (T) 0°C or 273 K
Standard pressure (P) 1 atm (760 mm Hg)
STP
Molar VolumeAt standard temperature and pressure
(STP), 1 mol of a gas occupies a volume of 22.4 L, which is called its molar volume.
The molar volume at STP can be used to form conversion factors.
22.4 L and 1 mol 1 mol 22.4 L
Molar Volume as a Conversion Factor
A. What is the volume at STP of 4.00 g of CH4?
B. How many grams of He are present in 8.00 L of gas at STP?
Learning Check
Important Simple Gas Relationships Boyles Law P1V1 = P2V2 (T fixed) Charles Law V1/T1 = V2/T2 (P fixed) Gay-Lussacs P1/T1 = P2/T2 (V fixed) Avogadros Law V1/n1 = V2/n2 (T&P fixed)
STP - Standard Temperature and Pressure (Gases)
T = 273 K (0 oC) and P = 1 atm (760 mmHg)1 mole of a gas at STP = 22.4L
Combined Gas Laws
Relates the changes in pressure, volume and temperature, and quantity change of a gas
PV = constant nT
Useful form of the expression:
P1V1 = P2V2
n1T1 n2T2
Combined Gas Law Practice A fixed quantity of nitrogen gas in a 275 mL
container at a pressure of 625 mm Hg is transferred to a container with a volume of 750. mL. What is the new pressure if the temperature changes from 25 oC to 17 oC?
Ideal Gas Law
Let’s now solve for the constant:
PV/nT = constant = R
One set of conditions we know - 1 mole of a gas at STP. (atm L/mol K)
The Ideal Gas Law
Describes the relationships among the four variables for gaseous substances: P, T, V, n PV = nRT
R is called the ideal gas constant 0.0821 atm·L/mol·K Always make sure you have all your units correct!
Gas Law Calculations What is the temperature (in oC) of a sample of 3.00 moles of He
at 27.5 atm of pressure and in a 6.00 L container?
A. 670.
B. 397
C.273
Gas Law Calculations Methane, CH4, can be used as fuel for an automobile; however, it is a
gas at normal temperatures and pressures, which causes some problems with storage. One gallon of gasoline could be replaced by 655 g of CH4. What is the volume of this much methane at 25 oC and 745 mm Hg.
A. 30.9
B. 510.
C.1020