Visualizing Molecular MotionFigure 6-14
Copyright © 2011 Pearson Canada Inc. General Chemistry: Chapter 6 Slide 1 of 41
6-7 Kinetic Molecular Theory of Gases
• Particles are point masses in constant,
random, straight line motion.
• Particles are separated by great
distances.
• Collisions are rapid and elastic.
• No force between particles.
• Total energy remains constant.
Gas Nonideal Behaviour
• Class discussion of evidence for.• Intermolecular forces.• Finite molecular size.• Condensed phases – they exist! (Cogito ergo
sum? H2O(g) liquefies therefore I am?) • V vs T graph for both ideal and real gases.
Synthetic Chemistry• Chemical reactions are used to transform
elements and simple compounds into more complex and important substances such as tetracycline (antibiotic), ammonium nitrate (fertilizer) and epitaxial silicon (computer chips). The synthetic chemistry of carbon is extremely varied. Nature produces complex organic molecules, often hydrocarbons, which can also be used as important energy sources.
Thermochemistry
• Chemical reactions can be employed to supply energy in various forms (usually heat, light and electricity).
• Eg. Ethanol – can be used as a solvent, as a synthetic building block or to provide energy through direct combustion, use in fuel cells, etc.
• C2H5OH(l) + 3O2(g) → 3CO2(g) + 3H2O(l)
• How much heat is released depends on the amount of ethanol burned and can be reported in kJ mol∙ -1, kJ∙ kg-1, etc. The quantity of heat produced will also vary with the temperature of the reactants and products as well as their phases.
• When one mole of C2H5OH is burned under constant pressure conditions about 726 kJ of energy are transferred (lost) to the surroundings.
• Write ΔHoCombustion = -726 kJ mol∙ -1
• In thermodynamics the system is a particular set of substances or objects being studied. The surroundings (of our system) is made up of the rest of the universe. There are three types of system.
• Open system – can exchange matter and energy with the surroundings. Closed system –can exchange energy but not matter with the surroundings. Isolated system – no exchange of matter or energy with the surroundings is possible (Hot coffee in a thermos bottle).
Slide 10 of 57
6-1 Getting Started: Some Terminology
Copyright © 2011 Pearson Canada Inc. General Chemistry: Chapter 7
FIGURE 7-1•Systems and their surroundings
Energy Units!• Energy units – usually joules, J, kJ, MJ.• 1 J = 1 kg m∙ 2 s∙ -2 and 1 calorie = 4.184 J (the
dietary calorie is 1000 times larger!)• Energy changes are associated with both
chemical and physical processes. For example, to melt a solid (fusion) or to vaporize a liquid energy must be supplied to our system.
• H2O(s) → H2O(l) ΔHoFusion = 6.01 kJ.mol-1
• H2O(l) → H2O(g) ΔHoVaporization = 44.0 kJ mol∙ -1
• Which process in important at “Tim’s” ?
Heating and Cooling Curves• Heating and cooling curves are simple to
construct unless there are phase changes to consider. In class we will construct two heating curves for constant pressure processes.
• Curve 1: Temperature vs heat supplied (q) for the heating of Al(s) from 15 OC to 111 OC.
• Curve 2: Temperature vs heat supplied for the transformation of ice at -45 OC to steam at a temperature of 165 OC.
Specific Heats• In drawing the two heating curves we
considered specific heats (specific heat capacities) – the amount of heat needed to raise the temperature of 1 g of a substance in a particular phase by 1 degree. We see
• q = mc∆t or q = ms∆t ……..• When employing these equations m, s and ∆t
must refer to a particular substance and a particular phase.