3 Characteristics of Gas Gases consist of Particles that are relatively far apartGas particles move very rapidlyGas particles have little interaction until they collide.Gases expand to fill the available space.
4 Description of GasesGases can be described in various physical properties.PressureTemperatureDensityVolumeNumber of ParticlesChanging one physical parameter will change one or more others.
5 Pressure Pressure (P) = Force/area There are several units for Pressure.Pounds/Sq. Inch (psi)1 Atmosphere (atm) = 760 mm Hg = 760 torr1 atm = 101,325 Pa (pascal)1 atm = 14.7 psi
6 EXAMPLECalculate the amount of pressure a 105 lbs. woman exerts by stepping down on a stiletto heel (1/16 sq inch)? Compare this to an Elephant (12,000 lbs., 16 sq. in. foot)?
7 PROBLEMThe depths of the ocean can exceed 380 atm of pressure. How many pascals is this? How many psi?
15 Kelvin ScaleSo far we have measured temperature in degrees Celsius, a relative scale.Absolute temperature is measure in Kelvin (K, note no degree sign is used), this scale is related to the absolute motion of atoms.0 K = °CTherefore Temp °C = Temp K
16 PROBLEM Calculate the following temperatures in Kelvin. Boiling Point of WaterFreezing Point of Water
17 PROBLEMGiven an ideal gas held at constant mass and pressure, what would be the temperature of the gas if it was originally at 125 °C, and its volume is dropped from 1.00 L to L?
18 Combined Gas LawCombining Boyle’s and Charles’s Law results in the following equation.𝑃 1 𝑉 1 𝑇 1 = 𝑃 2 𝑉 2 𝑇 2
19 PROBLEMA sample of Hydrogen gas occupies 1.25 L at 80.0 °C and 2.75 atm. What would its volume be at 185 °C and 5.00 atm?
20 Guy-Lussac and Avagadro Guy-Lussac’s Law stated that combined gases always reacted in small whole number ratios (sound familiar?)Avagadro hypothesized that the volume occupied by a gas is proportional to the number of gas particles and hence the moles of gas.
21 Avagadro’s Hypothesis At a given pressure and temperature, equal volumes of gas contain equal numbers of moles.Standard Temperature and Pressure (STP) are defined as K and 1 atm, at which 1.00 mole of gas occupies L, defined as molar volume
22 PROBLEMWhat volume would 1.00 mole of gas occupy at 37°C and 1.00 atm?
24 Review of the Relationships Boyle’s Law: (C is a constant)𝑉= 𝐶 𝑃 at constant n, TCharles’s Law:𝑉=𝐶𝑇 at constant n, PAvagadro’s Hypothesis:𝑉=𝐶𝑛 at constant P, T
25 Combine the EquationsAssume the constants combined equal another constant we will call the Ideal Gas Constant, R𝑉= 𝑅𝑛𝑇 𝑃Rearrange this into the Ideal Gas Law𝑷𝑽=𝒏𝑹𝑻
26 So What is the Value for R? Assuming a standard gas you can calculate the value of R𝑃𝑉=𝑛𝑅𝑇 becomes 𝑅= 𝑃𝑉 𝑛𝑇For a Standard gas mole at K and atm has a volume of L𝑅= (1.00 𝑎𝑡𝑚)×( 𝐿) (1.00 𝑚𝑜𝑙)×( 𝐾) = 𝐿∙𝑎𝑡𝑚 𝑚𝑜𝑙∙𝐾
27 PROBLEMCalculate the Ideal Gas Constant if pressure is measured in torr
28 PROBLEMThe volume of an oxygen cylinder is L. At a temperature of 32 °C the cylinder has a pressure of 945 torr. How many moles of Oxygen gas are in the cylinder?
29 PROBLEMGiven the amount of oxygen in the previous question, what is its mass?What is its density?
30 Partial PressuresDalton’s Law of Partial Pressure: Gases in a mixture behave independently and exert they same pressure as they would alone.𝑃 𝑚𝑖𝑥𝑡𝑢𝑟𝑒 = 𝑃 𝐴 + 𝑃 𝐵 + 𝑃 𝐶 …
31 PROBLEMGiven a L container at 45.00°C, what would be the total pressure in the container from a mixture of moles gaseous sulfur dioxide and moles hydrogen sulfide?
33 The return of Stoichiometry You can use the gas laws to solve stoichiometry problems by converting values between states of matter.
34 CuO(s) + H2(g) Cu(s) + H2O(g) ExampleA sample of hydrogen gas has a volume of 8.00 L at a pressure of 5.00 atm and a temperature of 25 °C. What volume of gaseous water is produced in the following reaction at °C and atm, if all the hydrogen gas reacts with copper (II) oxideCuO(s) + H2(g) Cu(s) + H2O(g)ALGORITHMmol of Hydrogen (PV=nRT)mol of Water (formula)V of Water (PV=nRT)
35 PROBLEMHow many grams of calcium carbonate is formed if 3.45 L of carbon dioxide, measured at 45.0 C and 1.37 atm, react with excess CaO? CaO(s) + CO2(g) CaCO3(S)