Intro to Gases Boyle’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 Gases Kinetic 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 = kPa = 760 mmHg = lb/in 2 Temperature: K = °C °C = K

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) P 1 V 1 = P 2 V 2 Charles’ Law: Volume and Temperature of a gas are directly proportional to each other. As temperature goes up, volume goes up (and visa-versa) V 1 / T 1 = V 2 / T 2

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. P Total = P 1 + P 2 + P 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 = 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 L/mol!

Closure State Boyle’s Law in your own words.