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Reactions that cause change of oxidation numbers are called redox reactions.

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## Reactions that cause change of oxidation numbers are called redox reactions.

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**Reactions that cause change of oxidation numbers**are called redox reactions. Element loses electrons → its oxidation number increases → element is oxidized → oxidation reaction Substance that contains the oxidized element is call the reducing agent. Element gains electrons → its oxidation number decreases → element is reduced → reduction reaction Substance that contains the reduced element is call the oxidizing agent.**2SO2 + O2 → 2SO3**.. • Write down the oxidation number for each • element above its symbol. • 2. Which element in what substance is oxidized? • Which element in what substance is reduced? • 3. What is the reducing agent? • What is the oxidizing agent?**Chapter 5**Gases**Four variables used to describe a gas**Amount — n — unit: mol Volume — V — unit: m3, L, mL Temperature — T — unit: °C, K Pressure — P — unit:**Pressure = Force / Area**Pa = N / m2 demo 1 atm = 760 mmHg = 760 torr = 101325 Pa e.g. 125 torr = ? atm = ? Pa 1 atm = pressure exerted by the air at 0 °C at sea level**Four variables used to describe a gas**Amount — n — unit: mol Volume — V — unit: m3, L, mL Temperature — T — unit: °C, K Pressure — P — unit: atm, torr, Pa**Volume of a gas equals the volume of the container in which**it is held because gas expands to fill the container.**Cu**Cu**Orange juice**Orange juice**Relationships among the four variables**Gas Laws P, V, T, n: study the relationship between two variables while keep the other two constant.**P V T n**Boyle’s Law Relationship between P and V under constant n and T.**Boyle’s Law**Relationship between P and V under constant n and T. PV = k**Boyle’s Law**P1V1 = P2V2 (1) (2)**P V T n**Charles’s Law Relationship between V and T under constant n and P.**Plots of V Versus T(°C) for Several Gases**2732 − 273 °C**Plots of V versus T as Before, Except Here the Kelvin Scale**is Used for Temperature**Charles’s Law**Relationship between V and T under constant n and P. V = bT or T must be in K**A sample of gas at 15 °C and 1 atm has a volume of 2.58 L.**What volume will this gas occupy at 38 °C and 1 atm?**P V T n**Avogadro’s Law Relationship between V and n under constant P and T.**V = an**Avogadro’s Law Relationship between V and n under constant P and T.**V = k/P**V = bT V = an Ideal Gas Law PV = nRT**Units in ideal gas law**PV = nRT Option 1 Chem 1211 P — atm, V — L, n — mol, T — K R = 0.082 atm · L · mol−1 · K−1 Option 2 P — Pa, V — m3, n — mol, T — K R = 8.314 J · mol−1 · K−1**Example 5.5, page 192**Calculate the volume occupied by 0.845 mol of nitrogen gas at a pressure of 1.37 atm and a temperature of 315 K.**A sample of diborane gas (B2H6) has a pressure of 345 torr**at a temperature of −15 °C and a volume of 3.48 L. How many B2H6 molecules are in this sample? If conditions are changed so that the temperature is 36 °C and the pressure is 468 torr, what will be the volume?**What is the volume in liters of exactly 1 mol ideal gas**at exactly 0 °C and 1 atm? 0 °C and 1 atm: standard temperature and pressure (STP) At STP, the volume of one mole ideal gas is 22.4 L**For a gas sample, the density is 1.95 g/L at 1.50 atm and**27 °C. What is the molar mass of the gas?**Example 5.7, page 195**Calculate the density of nitrogen gas at 125 °C and a pressure of 755 torr. d = 0.853 g/L**Dalton’s Law of partial pressure**The total pressure of a mixture of gases equals the sum of the pressures that each gas would exert if it were present alone. pressure that each gas would exert if it were present alone = partial pressure of that gas Pt = P1 + P2 + P3 + · · · = ntRT/V Each component and the whole gas mixture obey ideal gas law.**6.00 g O2 and 9.00 g CH4 are placed in a 15.0 L vessel**at 0 °C. What is the partial pressure of each gas and what is the total pressure? PO2 = 0.280 atm PCH4 = 0.837 atm Ptotal = 1.117 atm**6.00 g O2 and 9.00 g CH4 are placed in a 15.0 L vessel**at 0 °C. What is the partial pressure of each gas and what is the total pressure? PO2 = 0.280 atm PCH4 = 0.837 atm Ptotal = 1.117 atm What is the mole fraction of O2 in the mixture? A similar example on page 200. practice.**Air: 78 % N2, 21 % O2, 1 % other gases.**What is the partial pressure of N2 in torr?**The air on Pandora consists of N2, O2, CO2,**Xe, CH4, and H2S. The mole fractions of CO2 and H2S are 18 % and 1.0 %, respectively. If the partial pressure of CO2 is 164 torr, what is partial pressure of H2S in Pa?**The partial pressure of CH4(g) is 0.175 atm and that of**O2(g) • is 0.250 atm in a mixture of the two gases. • What is the mole fraction of each gas in the mixture? • If the mixture occupies a volume of 10.5 L at 65 °C, calculate • the total number of moles of gas in the mixture. • c) Calculate the mass of each gas in the mixture.**How is ideal gas law related**to chemical reactions?**aA + bB cC + dD**PV = nRT Link between a gas and chemical reaction**Example 5.12, page 203**Methanol (CH3OH) can be synthesized by the following reaction: CO(g) + 2H2(g) CH3OH(g) What volume (in liters) of hydrogen gas, at a temperature of 355 K and a pressure of 738 torr, is required to synthesize 35.7 g of methanol?**The metabolic oxidation of glucose, C6H12O6, in our bodies**produces CO2, which is expelled from our lungs as a gas: C6H12O6(aq) + 6O2(g) 6CO2(g) + 6H2O(l) Calculate the volume of CO2 produced at body temperature (37 °C) and 0.970 atm when 24.5 g of glucose is consumed in this reaction.**FOR PRACTICE 5.12, page 204**In the following reaction, 4.58 L of O2 was formed at P = 745 torr and T = 308 K. How many grams of Ag2O must have decomposed? 2Ag2O(s) 4Ag(s) + O2(g)**FOR PRACTICE 5.13, page 205**How many liters of oxygen (at STP) are required to form 10.5 g of H2O? 2H2(g) + O2(g) 2H2O(g)**What is the theory behind**ideal gas law?**Kinetic Molecular Theory**The size of gas molecules is assumed to be zero Gas molecules do not attract or repel each other Gas molecules constantly move, collisions with the wall of a container cause pressure Average kinetic energy of gas molecules is directly proportional to absolute temperature