Chapter 5 -Chapter 6

Chapter 5 -Chapter 6 - General Chemistry I Fall 2007 Joann...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: General Chemistry I Fall 2007 Joann S. Monko Chemistry 9th ed. Raymond Chang 2 KClO3 (s) 2 KCl (s) + 3 O2 (g) PTotal = PO2 + PH2O = atmospheric pressure Collection Apparatus Chemistry, 8th ed. Chang Pressure of Water Vapor Figure 5.16 Chemistry, 8th ed. Chang KINET IC MO LEC ULAR T HEO R Y (KMT ) Theory used to explain gas laws. KMT assumptions are... Gases consist of molecules in constant, random motion. P arises from collisions with container walls. No attractive or repulsive forces between molecules. Collisions elastic. Volume of molecules is negligible. Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. 0 Because we assume molecules are in motion, they have a kinetic energy. KE = (mass)(speed)2 = mu2 At the same T, all gases have the same average KE. As T goes up, KE also increases -- and so does speed. Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Kine tic Mo le c ula r T h e o ry 0 Dis trib utio n o f G a s Mo le c ule S pe e ds 0 Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Chemistry, 8th ed. Chang Ve lo c ity o f G a s Mo le c ule s 0 Molecules of a given gas have a range of speeds. Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Velocity of Gas Molecules 0 Average velocity decreases with increasing mass. Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. 0 Bo y le 's La w & G a s P re s s ure , Avo g a d ro 's T e m p e ra ture , Hy p o th e s is KMT & KMT & KMT P 1/V PT Pn Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. diffusion is the gradual mixing of molecules of different gases. G AS DIFFUS IO N AND EFFUS IO N 0 effusion is the movement of molecules through a small hole into an empty container. Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. 0 G AS DIFFUS IO N AND EFFUS IO N Molecules effuse thru holes in a rubber balloon, for example, at a rate (= moles/time) that is proportional to T inversely proportional to M. Therefore, He effuses more rapidly than O at same T. 2 Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. He Gas Diffusion relation of mass to rate of diffusion HCl and NH3 diffuse from opposite ends of tube. Gases meet to form NH4Cl HCl heavier than NH3 Therefore, NH4Cl forms closer to HCl end of tube. Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. 0 De via tio ns fro m Id e a l G a s La w Real molecules have volume. There are intermolecular forces. Otherwise a gas could not become a liquid. 0 Chemistry, 8th ed. Chang Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. De via tio ns fro m Id e a l G a s La w Account for volume of molecules and intermolecular forces with VAN DER WAAL'S EQUATION. Measured P Measured V = V(ideal) 0 ( P + n2a ----V2 ) V - nb nRT vol. correction intermol. forces Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. J. van der Waals, 1837-1923, Professor of Physics, Amsterdam. Nobel Prize 1910. De via tio ns fro m Id e a l G a s La w Measured P P + n2a ----V2 Measured V = V(ideal) V nb nRT 0 vol. correction intermol. forces Cl gas has a = 6.49, b = 0.0562 Table 5.4 Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. 2 Ene rg y & C h e m is try Burning peanuts supply energy to boil a cup of water. Burning sugar (sugar reacts with KClO3, a strong oxidizing agent) These reactions are PRODUCT FAVORED They proceed almost completely, perhaps with some outside assistance. Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Ene rg y & C h e m is try ENERGY is the capacity to do work or transfer heat. HEAT is the form of energy that flows between 2 objects because of their difference in temperature. Energy can be potential -- Chemical results from attractions among e-'s & atomic nuclei. Gravitational possessed by objects wrt position. Electrostatic results from attractions among + & - ions. Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Ene rg y & C h e m is try ENERGY is the capacity to do work or transfer heat. HEAT is the form of energy that flows between 2 objects because of their difference in temperature. Energy can be kinetic Thermal atoms/molecules in motion. Mechanical macroscopic objects in motion. Electric e-'s moving thru a conductor. Sound -changes in the space between molecules. Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. P o te ntia l Ene rg y Potential energy -- energy a motionless body has by virtue of its position. O n th e Ato m ic S c a le Positive and negative particles (ions) attract one another. Two atoms can bond As the particles attract they have a lower potential energy NaCl -- composed of Na+ and Clions. Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Kine tic Ene rg y Kinetic energy -- energy of motion Translation rotate vibrate translate Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Inte rna l Ene rg y (E) PE + KE = Internal energy (E or U) Int. E depends on number of particles type of particles temperature Higher T = Higher Internal Energy Use changes in T (T) to monitor changes in E (E). Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. T h e rm o d yna m ic s is the science of heat (energy) transfer. Heat energy is associated with molecular motions. Heat transfers until th e rm a l e q uilib rium is established. System the object(s) being studied. Surroundings everything outside that can exchange energy. Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Heat always transfers from a hotter object to a cooler one. Dire c tio na lity o f He a t T ra ns fe r EXOthermic: heat transfers from SYSTEM to SURROUNDINGS. T(system) goes down T(surr) goes up Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Directionality of Heat Transfer Heat always transfers from a hotter object to a cooler one. ENDOthermic: heat transfers from SURROUNDINGS to the SYSTEM. T(system) goes up T (surr) goes down Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Energy & Chemistry All of thermodynamics depends on the law of CONSERVATION OF ENERGY. Total energy is unchanged in a chemical rxtn. If PE of products is less than reactants, the difference is released as KE ... you feel a temperature increase. PE Reactants Kinetic Energy Products Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. UNITS OF ENERGY 1 calorie = heat required to raise temp. of 1.00 g of H2O by 1.0 oC. 1000 cal = 1 kilocalorie = 1 kcal 1 kcal = 1 Calorie (a food "calorie") But we use the unit called the JOULE or KILOJOULE 1 J = 1 kg m2/s2 1 cal = 4.184 joules Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. James Joule 1818-1889 Specific Heat Capacity How much energy is transferred due to T difference? The heat (q) "lost" or "gained" is related to a) b) c) sample mass change in T and specific heat capacity, SH Specific heat capacity = heat lost or gained by substance (J) (mass, g)(T change, K) SH = q . m T q = m SH T Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. T = Tfinal - Tinitial Specific Heat Capacity Substance Spec. Heat (J/gK) H2O 4.184 Ethylene glycol 2.39 Al 0.897 glass 0.84 Aluminum Which has the larger heat capacity? Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. If 25.0 g of Al cool from 310 oC to 37 oC, how many joules of heat energy are lost by the Al? heat gain/lose = q = (SH)(mass)(T) Specific Heat Capacity where T = Tfinal - Tinitial q = (0.897 J/gK)(25.0 g)(310 - 583)K q = - 6120 J Notice -the negative sign on q signals heat "lost by" or transferred OUT of Al. Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Clicker Question A one square mile lake is approx. 10 m deep = 2.6 x 1013 grams. What quantity of heat (in kJ) must be transferred to the lake water to raise the temperature by 1 C? The specific heat of water is 4.184 J/gK) Reading the Signs T = Tfinal - Tinitial q = m SH T T of System Sign Sign Direction of Process of of q Heat Transfer T + + From surroundings Endothermic to system From system to Exothermic surroundings Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Increase Decrease - - A 15.5 g piece of chromium, heated to 100C, is dropped into 55.5 g of water at 16.5C. The final temp. of the metal and water is 18.9C. What is the specific heat capacity of chromium? (Assume no heat is lost to the container or to the surrounding air.) The sum of thermal energy changes is zero. qwater and qmetal are = but opposite signs qwater = -qmetal qwater + qmetal = 0 (SH m T)water + (SH m T)metal = 0 (4.184 J/gK)(55.5 g)(18.9-16.5)K + SH(15.5 g)(18.9-100)K = 0 (4.184 J/gK)(55.5 g)(2.4K) + SH(15.5 g)(-81.1K) = 0 557 J + SH(-1257gK) = 0 557 J = SH(1257gK) Kotz &Treichel Chemistry & Chemical Reactivity SH of the metal = 0.443 J/gK 5th ed. Clicker Question Determine the specific heat capacity of a piece of metal A 55.0 g sample was heated to 99.8 C and then put into 225 g of water at 21 C. The final temperature of the water and metal was 23.1 C. (Answer to 3 decimal places) ...
View Full Document

Ask a homework question - tutors are online