11.4-11.5 Tro's Introductory Chemistry, Chapter 11

Boyle’s Law Pressure of a gas is inversely proportional to its volume. Constant T and amount of gas. Graph P vs. V is curved. Graph P vs. 1/V is in a straight line. As P increases, V decreases by the same factor. P x V = constant. P1 x V1 = P2 x V2 . Tro's Introductory Chemistry, Chapter 11

Boyle’s Experiment Added Hg to a J-tube with air trapped inside. Used length of air column as a measure of volume. Tro's Introductory Chemistry, Chapter 11

Tro's Introductory Chemistry, Chapter 11

Tro's Introductory Chemistry, Chapter 11

Boyle’s Experiment, P x V Tro's Introductory Chemistry, Chapter 11

When you double the pressure on a gas, the volume is cut in half (as long as the temperature and amount of gas do not change). Tro's Introductory Chemistry, Chapter 11

Gas Laws Explained— Boyle’s Law Boyle’s law says that the volume of a gas is inversely proportional to the pressure. Decreasing the volume forces the molecules into a smaller space. More molecules will collide with the container at any one instant, increasing the pressure. Tro's Introductory Chemistry, Chapter 11

A Cylinder with a Movable Piston Has a Volume of 6. 0 L at 4. 0 atm A Cylinder with a Movable Piston Has a Volume of 6.0 L at 4.0 atm. What Is the Volume at 1.0 atm?

A Balloon Is Put in a Bell Jar and the Pressure Is Reduced from 782 torr to 0.500 atm. If the Volume of the Balloon Is Now 2780 mL, What Was It Originally? Tro's Introductory Chemistry, Chapter 11

Temperature Scales Celsius Kelvin Fahrenheit Rankine 100°C 373 K 212°F BP Water 0°C 273 K 32°F 459 R MP Ice -38.9°C 234.1 K -38°F 421 R BP Mercury -183°C 90 K -297°F 162 R BP Oxygen BP Helium -269°C 4 K -452°F 7 R -273°C 0 K -459 °F 0 R Absolute Zero Celsius Kelvin Fahrenheit Rankine

Gas Laws and Temperature Gases expand when heated and contract when cooled, so there is a relationship between volume and temperature. Gas molecules move faster when heated, causing them to strike surfaces with more force When doing gas problems, always convert your temperatures to kelvins. K = °C + 273 °F = 1.8 °C + 32 & °C = 0.556(°F-32) Tro's Introductory Chemistry, Chapter 11

Standard Conditions Common reference points for comparing. Standard pressure = 1.00 atm. Standard temperature = 0 °C. 273 K. STP. Tro's Introductory Chemistry, Chapter 11

Volume and Temperature In a rigid container, raising the temperature increases the pressure. For a cylinder with a piston, the pressure outside and inside stay the same. To keep the pressure from rising, the piston moves out increasing the volume of the cylinder. As volume increases, pressure decreases. Tro's Introductory Chemistry, Chapter 11

Volume and Temperature, Continued As a gas is heated, it expands. This causes the density of the gas to decrease. Because the hot air in the balloon is less dense than the surrounding air, it rises. Tro's Introductory Chemistry, Chapter 11

Charles’s Law Volume is directly proportional to temperature. Constant P and amount of gas. Graph of V vs. T is a straight line. As T increases, V also increases. V = constant x T. If T is measured in kelvin. Tro's Introductory Chemistry, Chapter 11

Absolute Zero Theoretical temperature at which a gas would have zero volume and no pressure. Kelvin calculated by extrapolation. 0 K = -273.15 °C = -459 °F Never attainable. Though we’ve gotten real close! All gas law problems use the Kelvin temperature scale. Tro's Introductory Chemistry, Chapter 11

Determining Absolute Zero William Thomson, the Lord of Kelvin, extrapolated the line graphs of volume vs. temp- erature to determine the theoretical temperature that a gas would have given a volume of 0. Tro's Introductory Chemistry, Chapter 11

A Gas Has a Volume of 2. 57 L at 0 °C. What Was the Temperature at 2 A Gas Has a Volume of 2.57 L at 0 °C. What Was the Temperature at 2.80 L?

The Temperature Inside a Balloon Is Raised from 25. 0 °C to 250. 0 °C The Temperature Inside a Balloon Is Raised from 25.0 °C to 250.0 °C. If the Volume of Cold Air Was 10.0 L, What Is the Volume of Hot Air? Tro's Introductory Chemistry, Chapter 11