Section 13.1 Describing the Properties of Gases 1.To learn about atmospheric pressure and how barometers work 2.To learn the units of pressure 3.To understand how the pressure and volume of a gas are related 4.To do calculations involving Boyle’s Law 5.To learn about absolute zero 6.To understand how the volume and temperature of a gas are related 7.To do calculations involving Charles’s Law 8.To understand how the volume and number of moles of a gas are related 9.To do calculations involving Avogadro’s Law 10.To understand how the temperature and pressure of a gas are related. 11.To do calculations involving Gay-Lussac’s Law. Objectives

Section 13.1 Describing the Properties of Gases Units involved in Gas Laws (memorize these) Volume liters (L) milliliters (mL) centimeters cubed (cm 3 ) decimeters cubed (dm 3 ) Temperature degrees Celsius (°C) Kelvins (K) –used primarily Pressure atmospheres (atm) Pascals (Pa) kilopascals (kPa) pounds per square inch (psi) millimeters of mercury (mmHg) Torricellis (torr) Standard Temperature & Pressure (STP) 0°C and 1 atmosphere

Section 13.1 Describing the Properties of Gases Barometer – device that measures atmospheric pressure –The weight of the air pushing down on the open dish of mercury supports a column of mercury in a closed tube Measuring Pressure Pressure – the force a gas exerts (per unit area) on its surroundings Gas pressure is caused by gas molecules colliding with the surfaces of the surrounding substances.

Section 13.1 Describing the Properties of Gases A. Pressure –Changing weather conditions Atmospheric Pressure

Section 13.1 Describing the Properties of Gases A. Pressure –Changing altitude Atmospheric Pressure

Section 13.1 Describing the Properties of Gases A. Pressure 1 standard atmosphere of air pressure = atm = lbs / in 2 (psi) = mm Hg = torr = 101,325 Pa = kPa Units of Pressure

Section 13.1 Describing the Properties of Gases A. Pressure Measuring Pressure A manometer measures the pressure of a gas trapped in a container. What would the manometer look like if the gas pressure inside were equal to atmospheric pressure?

Section 13.1 Describing the Properties of Gases Robert Boyle’s experiment –a certain amount of gas is trapped in a J-tube –as more mercury is added, the trapped gas is compressed into a smaller volume the same number of gas molecules in a smaller volume = more frequent collisions Higher pressure B. Pressure and Volume: Boyle’s Law (when temperature (T) and amount of gas (n) are constant!)

Section 13.1 Describing the Properties of Gases B. Pressure and Volume: Boyle’s Law

Section 13.1 Describing the Properties of Gases Graphing Boyle’s results –as volume of the gas increases the pressure on the gas decreases more space = fewer collisions –as the volume of the gas decreases, pressure on the gas increases smaller space = more collisions B. Pressure and Volume: Boyle’s Law

Section 13.1 Describing the Properties of Gases B. Pressure and Volume: Boyle’s Law This graph has the shape of half of a hyperbola Volume and pressure are inversely proportional. –If one increases the other decreases. more space=few collisionslittle space=more collisions

Section 13.1 Describing the Properties of Gases B. Pressure and Volume: Boyle’s Law Another way of stating Boyle’s Law is P 1 V 1 = P 2 V 2 (constant temperature and amount of gas (moles))

Section 13.1 Describing the Properties of Gases When the pressure of a gas is kept constant –As the temperature increases, gas molecules travel faster. –They collide with each other with much more force –The collision force them to bounce off each other a greater distance –The gas molecules spread out a lot fill more volume C. Volume and Temperature: Charles’s Law

Section 13.1 Describing the Properties of Gases Graphing data for several gases –as temperature increases, volume increases Temperature and Volume are directly proportional to one another –if one increases, the other also increases T must be converted to Kelvins C. Volume and Temperature: Charles’s Law (when pressure and amount of gas (moles) are constant!)

Section 13.1 Describing the Properties of Gases It is easier to write an equation for the relationship if we make the lines intersect the origin of the graph (0 and 0). –so we invented a new temperature scale (Kelvins) 0 Kelvins is called absolute zero At absolute zero, a gas has no volume (theoretically) C. Volume and Temperature: Charles’s Law

Section 13.1 Describing the Properties of Gases C. Volume and Temperature: Charles’s Law Volume and temperature are directly proportional. –If one increases the other increases. Another way of stating Charles’s Law is constant pressure (P) and amount of gas (n) CAUTION: temperature must be expressed in Kelvins (absolute temperature) if not, convert it to Kelvins K temp = °C temp + 273

Section 13.1 Describing the Properties of Gases D. Volume and Moles: Avogadro’s Law (when temperature and pressure are constant!)

Section 13.1 Describing the Properties of Gases D. Volume and Moles: Avogadro’s Law Volume of a gas is directly proportional to number of moles (amount) of gas –If one increases the other increases. –at a constant temperature and pressure Another way of stating Avogadro’s Law is (constant temperature and pressure)

Section 13.1 Describing the Properties of Gases E. Temperature and Pressure: Gay-Lussac’s Law (when volume and amount of gas (moles) are constant!) Temperature and Pressure are directly proportional to one another. As the temperature increases, gas molecules travel faster. They collide with each other and the walls of the container more often, and with greater force –more frequent & violent collisions = more pressure

Section 13.1 Describing the Properties of Gases Pressure inversely proportional to Volume –Boyle’s Law Volume directly proportional to Absolute Temperature –Charles’s Law Volume directly proportional to Moles of gas –Avogadro’s Law Pressure directly proportional to Absolute Temperature –Gay-Lussac’s Law Summary of Measurable Gas Properties