Presentation on theme: "Unit 9 - States of Matter and Gas Behavior"— Presentation transcript:
1Unit 9 - States of Matter and Gas Behavior Chemistry Chapters 12-13
2The Behavior of GasesGases expand, diffuse, exert pressure, and can be compressed because they are in a low density state consisting of tiny, constantly-moving particles.Kinetic-molecular theory explains the different properties of solids, liquids, and gases.Atomic composition affects physical and chemical properties.The kinetic-molecular theory describes the behavior of matter in terms of particles in motion.
3The Behavior of GasesGases consist of small particles separated by empty space.Gas particles are too far apart to experience significant attractive or repulsive forces.Gas particles are in constant random motion.An elastic collision is one in which no kinetic energy is lost.Kinetic energy of particles is directly proportional to temperature
4The Behavior of GasesKinetic energy of a particle depends on mass and velocity.Temperature is a measure of the average kinetic energy of the particles in a sample of matter.
5The Behavior of GasesGreat amounts of space exist between gas particles.Compression reduces the empty spaces between particles.
6Gas Pressure Pressure is defined as force per unit area. Gas particles exert pressure when they collide with the walls of their container.The particles in the earth’s atmosphere exert pressure in all directions called air pressure.There is less air pressure at high altitudes because there are fewer particles present, since the force of gravity is less.
7Gas PressureBarometers are instruments used to measure atmospheric air pressure.
8Gas PressureThe average height of a mercury column in a barometer at sea level is 760 mm (760 mmHg)There are other units of pressure as well with the following relationships:1.00 atm = 760 mmHg = 760 torr = kPa
9Gas PressureDalton’s law of partial pressures states that the total pressure of a mixture of gases is equal to the sum of the pressures of all the gases of the mixture.The partial pressure of a gas depends on the number of moles, size of the container, and temperature and is independent of the type of gas.
10Gas Pressure Ptotal = P1 + P2 + P3 +…Pn Partial pressure can be used to calculate the amount of gas produced in a chemical reaction.
11Gas PressureGases are often collected by water displacement, but water vapor is introduced to the gas sample (mixture of gases)You can use Dalton’s law to get the partial pressure of the gas without the water vapor
12Forces of AttractionIntermolecular forces—including dispersion forces, dipole-dipole forces, and hydrogen bonds—determine a substance’s state at a given temperature.Attractive forces between molecules cause some materials to be solids, some to be liquids, and some to be gases at the same temperature.
13Forces of AttractionPrefix INTRA means “within”, where INTER means “between”
14Forces of AttractionDispersion forces are weak forces that result from temporary shifts in the density of electrons in electron clouds.Weakest of all intermolecular forcesDispersion forces become increasingly stronger as molecule gets more electrons, which explains why iodine is a solid but fluorine is a gas at room temperature
15Forces of AttractionDipole-dipole forces are attractions between oppositely charged regions of polar molecules.
16Forces of AttractionHydrogen bonds are special dipole-dipole attractions that occur between molecules that contain a hydrogen atom bonded to a small, highly electronegative atom with at least one lone pair of electrons, typically fluorine, oxygen, or nitrogen.
18Liquids and SolidsThe particles in solids and liquids have a limited range of motion and are not easily compressed.Liquids and solids are called “condensed phases” because their particles are very close together and do not have the energy necessary to “escape” the sample…their motion is limited
19Liquids and SolidsSolid particles are arranged in a crystal arrangement where they are fixed in position.This arrangement results in a substance that has a defined shape and volume.
20Liquids and SolidsLiquid particles have enough energy to “slide” by other particles, but do not have the energy to escape the sample itself.This results in a substance that has a fixed volume but takes the shape of its container.
21Phase ChangesMatter changes phase when energy is added or removed.Heat is the transfer of energy from an object at a higher temperature to an object at a lower temperature.
22Phase ChangesWhen ice is heated, the ice eventually absorbs enough energy to break the hydrogen bonds that hold the water molecules together.When the hydrogen bonds break, the particles move apart and ice melts into water.The melting point of a crystalline solid is the temperature at which the forces holding the crystal lattice together are broken and it becomes a liquid.
23Phase ChangesVaporization is the process by which a liquid changes to a gas or vapor.Evaporation is vaporization only at the surface of a liquid.
24Phase ChangesIn a closed container, the pressure exerted by a vapor over a liquid is called vapor pressure.
25Phase ChangesThe boiling point is the temperature at which the vapor pressure of a liquid equals the atmospheric pressure.
26Phase Changes Evaporation vs Boiling Summary: Evaporation is the result of surface level molecules obtaining enough energy to escape the sample as a gasBoiling occurs throughout the sample when the vapor pressure of the liquid is the same as the atmospheric pressure
27Phase ChangesSublimation is the process by which a solid changes into a gas without becoming a liquid.As heat flows from water to the surroundings, the particles lose energy.The freezing point is the temperature at which a liquid is converted into a crystalline solid.As energy flows from water vapor, the velocity decreases.The process by which a gas or vapor becomes a liquid is called condensation.Deposition is the process by which a gas or vapor changes directly to a solid, and is the reverse of sublimation.
28Phase ChangesA phase diagram is a graph of pressure versus temperature that shows in which phase a substance will exist under different conditions of temperature and pressure.
30Phase ChangesThe triple point is the point on a phase diagram that represents the temperature and pressure at which all three phases of a substance can coexist.The critical point is the highest temperature the substance can exist as a liquid, regardless of pressureNormal melting point and Normal boiling point are the temperatures at which these phase changes occur under standard pressure (760 torr)
31Gas LawsFor a fixed amount of gas, a change in one variable—pressure, temperature, or volume—affects the other two.
32Gas LawsBoyle’s law states that the volume of a fixed amount of gas held at a constant temperature varies inversely with the pressure.P1V1 = P2V2 where P = pressure and V = volume
33Gas LawsExample Problem. A sample of oxygen gas has a volume of 150. mL when its pressure is atm. What will the volume of the gas be at a pressure of atm if the temperature is constant?
34Gas LawsGivens and UnknownP1=0.947 atmV1=150. mLP2=0.987 atmV2=?
35Gas LawsEquation P1V1=P2V2Solve for unknown, V2
36Gas LawsAs temperature increases, so does the volume of gas when the amount of gas and pressure do not change.Kinetic-molecular theory explains this property.
38Gas LawsCelsius and Fahrenheit use ARBITRARY zero points, where any temperature lower than these points are considered to be negativeAbsolute zero is zero on the Kelvin scale.Remember - temperature is a measure of kinetic energy of the particles. Particles CAN NOT HAVE less kinetic energy than zero. Therefore, at absolute zero, all motion ceases.
39Gas Laws Conversions: Kelvin T (K) = Celsius T (C) + 273 Celsius T (C) = Kelvin T (K) - 273
40Gas LawsCharles’s law states that the volume of a given amount of gas is directly proportional to its kelvin temperature at constant pressure.
41Gas LawsIMPORTANT! Your temperatures MUST BE IN KELVIN when using Charles’ Law (or any gas law).A rearrangement of the Charles’ Law equation that is often easier to use (no fraction) is V1T2=V2T1
42Gas LawsExample - A sample of oxygen gas has a volume of 150. mL when its temperature is 295 K. What will the volume of the gas be at a temperature of 309 K if the pressure is constant?
43Gas LawsGivens and UnknownV1=150. mLT1=295 KV2=?T2=309 K
50Gas LawsThe combined gas law states the relationship among pressure, temperature, and volume of a fixed amount of gas.We can rearrange the equation to remove the fraction and get P1V1T2=P2V2T1
51Gas LawsExample: A balloon is inflated to 20.0 L at 31 deg C and 89.0 kPa. Determine the new volume of the balloon if it is brought to conditions of 4 deg C and kPa.P1 = 89.0 kPaV1 = 20.0 LT1 = 31 deg C = 304 KP2 = kPaV2 = ?T2 = 4 deg C = 277 K
52Gas LawsP1V1T2 = P2V2T1…solve for V2V2 = P1V1T2/P2T1
53The Ideal Gas LawThe ideal gas law relates the number of particles to pressure, temperature, and volume.Avogadro’s principle states that equal volumes of gases at the same temperature and pressure contain equal numbers of particles.
54The Ideal Gas LawThe molar volume of a gas is the volume 1 mol occupies at 0.00°C and 1.00 atm of pressure.0.00°C and 1.00 atm are called standard temperature and pressure (STP).At STP, 1 mol of gas occupies 22.4 L.
55The Ideal Gas LawIdeal gas particles occupy a negligible volume and are far enough apart to exert minimal attractive or repulsive forces on each other.Combined gas law to ideal gas law
56The Ideal Gas LawThe ideal gas constant is represented by R and is L•atm/mol•K when pressure is in atmospheres. It is expressed as L•kPa/mol•K when pressure is in kilopascalsThe ideal gas law describes the physical behavior of an ideal gas in terms of pressure, volume, temperature, and amount.We call the constant “R”
57The Ideal Gas LawTo rearrange this equation to get rid of the fraction, we get the most common expression of the lawPV = nRTn = number of moles
58The Ideal Gas LawRemember! The ideal gas law DOES NOT deal with changing conditions. Given three of the four variables that describe a gas, you can solve for the fourth!
59The Ideal Gas LawSample Problem - A sample of carbon dioxide with a mass of g was placed in a 350 mL container at 127 deg C. What is the pressure exerted by the gas in kPa?P = ?V = 350 mL x (1L/1000mL) = 0.35 LN = g x (1 mole/44.01g) = molR = LkPa/(Kmol)T = 127 C = 400. K
61Ideal Gas LawYou Try: An oxygen sample has a volume of 4.0 L at 37C and atm. Calculate the number of moles of oxygen in the sample.
62Ideal Gas Law P = 1.086 atm V = 4.0 L N = ? R = 0.08206 Latm/(Kmol) T=310 KPV=nRT, n=PV/RT
63Real GasesIdeal gases follow the assumptions of the kinetic-molecular theory.Ideal gases experience:There are no intermolecular attractive or repulsive forces between particles or with their containers.The particles are in constant random motion.Collisions are perfectly elastic.No gas is truly ideal, but most behave as ideal gases at a wide range of temperatures and pressures.
64Real GasesReal gases deviate most from ideal gases at high pressures and low temperatures.Polar molecules have larger attractive forces between particles.Polar gases do not behave as ideal gases.Large nonpolar gas particles occupy more space and deviate more from ideal gases.
65Gas StoichiometryWhen gases react, the coefficients in the balanced chemical equation represent both molar amounts and relative volumes.The gas laws can be applied to calculate the stoichiometry of reactions in which gases are reactants or products.
66Gas Stoichiometry 2H2(g) + O2(g) → 2H2O(g) 2 mol H2 reacts with 1 mol O2 to produce 2 mol water vapor.Coefficients in a balanced equation represent volume ratios for gases.
67Gas Stoichiometry Solving Volume to Volume Problems Volume of a gas is DIRECTLY PROPORTIONAL to the number of moles.Since volume is dependant on temperature, pressure, and moles, and NOT TYPE OF GAS, then a VOLUME RATIO can be used INSTEAD of a mole ratio.
68Gas Stoichiometry 3 H2 (g) + N2 (g) 2 NH3 (g) If 2.0 L of hydrogen reacts with excess nitrogen, calculate the volume of ammonia produced in L at 20 deg C and kPa.
69Gas Stoichiometry Solving other types of Gas Stoichiometry Problems Unless Volume - Volume, you must always use a MOLE RATIO.YOU GOTTA BE IN MOLES TO USE THAT MOLE RATIO!GOT MOLES?
70Gas StoichiometryWhen given the volume of a gas, use the ideal gas law to find MOLES of the gas.2 Cu2S + 3 O2 2 Cu2O + 2 SO2What mass of copper (I) sulfide is required to react completely with 46.6 L of Oxygen at 25°C and kPa?
71Gas StoichiometryWhen given an amount other than volume of a gas and asked to SOLVE for volume of a gas, first solve for MOLES of the gas (using stoichiometry relationships), then use ideal gas law to solve for volume.
72Gas Stoichiometry CH4 (g) + 2 O2 (g) CO2 (g) + 2 H2O (g) What volume of oxygen gas at 29°C at 1.06 atm is needed for the combustion of 6.25 g of methane?
73Gas StoichiometryWhen you are at STP, you can use the molar volume of a gas and avoid using the ideal gas law altogether!2 H2O (l) 2 H2 (g) + O2 (g)If 25.0g of water is decomposed, what volume of oxygen gas is produced at STP?Remember! Molar volume of any gas at STP = 22.4 L/mol!