Chemistry 0 Unit B Basses Molar Volume of Basses aw of Combined Volumes The Ideal Bass aw Chemistry 0 Unit B Gases Molar Volume of Gases aw of Combined Volumes The Ideal Gas aw Nov 0 7:34 AM Oct 10 3:36 PM Dr. Martyn Poliakoff Proudly Presents: http://www.periodicvideos.com/# The Periodic Table Movie of the Day!!! POS Checklist eplain the law of combining volumes. illustrate how Boyle's Charles' laws, individually combined, are related to the ideal gas law PV = nrt Oct 10 3:3 PM Oct 10 3:3 PM Review: 1. What are the four tenants (main points) of the particle theory (kinetic molecular theory)?. Qualitatively eplain, in terms of the particle theory, Boyle's aw Charles' aw. 3. What is meant by SATP STP? 4. What about when gases combine? What's up with that? Combining Gases proposed in 1808 by Joseph Guy ussac comes out of measuring relative volumes of gases involved in chemical reactions He found that: + yields: 5. Has the identity of the gas mattered at all up till now? Does that seem totally weird to you? 1 of Cl (g) 1 of H (g) of HCl (g) Oct 10 3:39 PM Oct 10 3:50 PM 1
+ 1 of Cl (g) 1 of H (g) yields: of HCl (g) aw of Combining Volumes When measured at the same temperature pressure, gases combine in simple whole number ratios. This follows the coefficients in the balanced chemical equation perfectly: 1 Cl (g) + 1 H (g) HCl (g) e) The formation of ammonia: 1 N (g) + 3 H (g) NH 3(g) 10 30 0 Oct 10 3:56 PM Oct 10 3:4 PM e) In a hydrogen fuel cell, H (g) is combusted with oygen to form water vapour. a) Write the balanced chemical equation for this reaction. b) If of oygen is used, what volume of H will react? What volume of water will be produced? Step 1: Write a balanced equation. H (g) + O (g) H O (g) Step : Write a ratio of the unknown : known for the coefficients volumes of the substances. H = = O 1 coefficients volumes Oct 10 4:10 PM Oct 10 4:13 PM Step 3: Algebraically solve for the unknown. 1 = = 8.0 Step 4: Repeat as needed to find volumes of other species. H O = = O 1 coefficients volumes = 8.0 e) In any oyacetylene welder, oygen acetylene are combined in a hydrocarbon combustion: O (g) + C H (g) CO (g) + H O (g) If 3.5 of oygen is used, how much carbon dioide is produced? How much water is produced? How much acetylene is used up? Tip: Species with the same coefficients produce the same volumes. Oct 1 :58 PM Oct 10 4:00 PM
Important Note: This law only applies to gases at the same temperature pressure! Measuring Gases: So far, we've measured gases using the following quantities: P = pressure (kpa, atm, mmhg, torr, psi) V = volume () T = temperature ( o C, K) However, there is another important quantity that we use to measure chemicals that is missing here... Oct 1 3:05 PM Oct 1 3:06 PM Molar Volume Recall that Avogadro said: One mole of any substance contains 6.0 10 3 atoms. that: n = m M n = # of moles m = mass of substance M = molar mass of substance Our old friend Dalton said we could... but because the mass of a gas is difficult to measure*, Dalton developed the idea of molar volume. Molar Volume: the number of moles per unit of volume in a gas. Can we apply this idea to gases? *Challenger question: how could we determine the mass of a gas? ANS change their state density momentum Oct 1 3:09 PM Oct 1 3:14 PM To determine molar volume, we use an equation strikingly similar to the molar mass equation: n = v V where: n = number of moles (mol) v = volume () V = molar volume (mol/) But there is a major difference between the idea of molar mass molar volume... We can calculate the molar mass of a chemical using values on the periodic table: There are no values for molar volumes. (One mole of iron has a mass of 55.85 grams.) Nov 0 8:07 AM Oct 1 3: PM 3
uckily, Avogadro has taken care of this for us too. Equal volumes of gases at the same temperature pressure contain equal numbers of molecules. This means that 1.0 of nitrogen has the same number of molecules ( therefore the same number of moles) as 1.0 of oygen, or helium, or plutonium, or any other gas would have. This Any gas at the same pressure, temperature volume will have the same number of moles per litre. The empirically deduced conversion factor for the molar volume of any gas at SATP is V = 4.8 /mol SATP or, for STP V =.4 /mol STP Oct 1 3:1 PM Nov 0 8:19 AM e) What volume of gas is present in a sample containing 0.50 mol at SATP? e) What volume of gas does 3.50 g of helium occupy at SATP? Oct 10 3:49 PM Oct 1 3:34 PM Ideal Gas aw As long as we are talking about moles, we might as well build an equation that allows us to work with volume, pressure, temperature pressure along with moles. This gives us an equation that can be used to deal with all of the quantities that define a gaseous system: You know how this goes: V1 = V T1 T charles' law P1V1 = PV boyle's law V α n molar volume PV = nrt where: R = the Universal Gas Constant To determine the value of R, we simply substitute in the SATP or STP values. Oct 1 3:40 PM Oct 1 3:51 PM 4
e) Determine the value of R at SATP (use data booklet values, recall that 1.0 mol = 4.8 ). Note: depending on the units used, different values of R can be obtained. You must determine what value will work for the units you are using in a particular question. All values will be given on eams. Ans: 8.314 kpa/kmol (also found in data booklet) Oct 1 3:54 PM Oct 1 4:19 PM Speaking of basses, what's your idea of an ideal bass? I mean, what is an ideal gas? An ideal gas obeys all the gas laws perfectly does not condense when cooled. In reality, no gases are real gases, but nearly all gases behave like real gases at SATP STP. We consider all gases in Chem 0 ideal gases. HW: Molar Volume, aw of Combining Volumes, Ideal Gas aw Assignment Oct 1 3:35 PM Oct 1 3:58 PM 5