Intro to Gases Boyle’s Law Lab Chemistry 4/16/15.
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Transcript of Intro to Gases Boyle’s Law Lab Chemistry 4/16/15.
Intro to GasesBoyle’s Law Lab
Chemistry 4/16/15
Drill
New packet!
How are gases different from solids and liquids?
How can you describe a gas?
HW: Finish 13-2 Practice Probs (pg. 2)
Objectives
IWBAT Describe gases by their properties Discover the mathematical relationships in
Boyle’s Law.
Agenda
Drill
Intro to Gases Notes (front of note sheet)
Pressure conversions
Closure
Physical Characteristics
of GasesKinetic Molecular Theory
Kinetic Molecular Theory of Gases
The kinetic molecular theory of matter (KMT) is based on the idea that particles of gases are always in motion.
The KMT assumes that a gas is ideal: An ideal gas is an imaginary gas that fits all the
assumptions of KMT. Ideal gases are NOT real, but gases behave like ideal
gases when pressure is not high and temperature is not low. What happens when pressure is high or when
temperature is low?
Assumptions of KMT
Gases consist of large numbers of tiny particles that are far apart from each other relative to their size.
Collisions between gas particles and other things are completely elastic -- no energy is lost.
Gas molecules are in constant, rapid motion.
There is no attraction or repulsion between gas molecules.
The average kinetic energy of gas molecules depends on the temperature of the gas.
Physical Properties of
Gases Expansion -- no definite shape or volume
Fluidity -- flows freely
Low density
Compressibility -- may be crowded together
Diffusion -- spontaneous mixing of two gases
Effusion -- particles under pressure can leak out of a tiny opening
Standard Temperature and Pressure (STP): 1 atm, 273K
Units and Equipment for Measuring Gases
Units: Pressure:
Atmospheres (atm)
Pascals (Pa) Millimeters of
mercury (mmHg) Volume
Liters or milliliters (L or mL)
Amount of the Gas Moles (mol)
Temperature Kelvin (K) NOT Celsius or
Fahrenheit
Equipment: Pressure:
Pressure gauge Barometer
What is air pressure?
Air pressure is the weight of the air pressing down on an object.
Air presses in all directions, with the same amount – about 760 mmHg.
Conversions
We will frequently need to convert between different measurements, especially for pressure: 1 atm = 101.325 kPa = 760 mmHg = 14.69
lb/in2
Temperature: K = °C + 273.15 °C = K - 273.15
Practice with Conversion
Let’s practice with 13-2 Practice Problems #1-8 – conversions of pressure measurements.
Let’s review
The Gas Laws: Boyle’s and
Charles’ Boyle’s Law:
Pressure and Volume of a gas are indirectly proportional to each other.
As pressure goes up, volume goes down (and visa-versa)
P1V1 = P2V2
Charles’ Law: Volume and Temperature of a gas are
directly proportional to each other. As temperature goes up, volume goes up
(and visa-versa) V1/ T1 = V2 / T2
The Gas Laws: Gay-Lussac’s and
Combined
Gay-Lussac’s Law: Pressure and temperature of a gas
are directly proportional to each other.
As temperature goes up, so does the pressure (and visa-versa)
P1 / T1 = P2 / T2
The Combined Gas Law: P1V1 = P2 V2 T1 T2
The Gas Laws:Dalton’s and
Graham’s
Dalton’s Law of Partial Pressures The pressures of mixed gases add together. PTotal = P1 + P2 + P3 + ...
Graham’s Law Compares the rates of diffusion of any two gases using the
following equation: Ms. Bloedorn will write it on the board
Moles and Gases As you increase the amount of a gas (moles), the
volume increases too.
Avogadro’s Law: V1 = V2 n1 n2 It is rarely used in this form.
Ideal Gas Law: PV = nRT R = 0.0821 L • atm mol • K
Moles and Gases, cont.
If all gases act the same way, would the volume of a mole of any gas be the same at STP? YES!
The standard molar volume of a gas (volume of 1 mol at STP) is 22.4 L.
22.4 L/mol!
Closure
State Boyle’s Law in your own words.