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David Mc Millen

PHYSICAL CHEMISTRY 2e [Thomas Engel, Philip Reid] CHAPTER 1 Thermochemistry - Branch of science that describes the behaviour of matter and the transformation between different forms of energy on amacroscopic scale (measurement);only a few such variables needed to describe a system of interest Eg. 1 molof gaseous water is described by three macroscopic variables, pressure, volume and temperature. One the microscopic scale by contrast refers to dimensions on order of the molecular size eg. H2O a dipolar triatomic molecule with a B.A at 104.5 degrees Statistical thermodynamics uses atomics/molecular properties to calculate macroscopic properties. Basic definitions describing Thermodynamic systems  System consists of all materials in the process involved in the process under study. Eg. Open beaker with reagents Electrolyte solution with an electrochemical cell Contents of a cylinder with movable piston Rest of the universe is referred to as the surroundings 2 types of systems 1. Open System – a system that can exchange matter with surroundings eg. Animal vs. Plant cells 2. Closed Sytem – a system that cannot exchange matter with surroundings as open systems { BOTH SYSTEMS CAN EXCHANGE MATTER WITH SURROUNDINGS} A system that can do neither is an isolated system  The interface between the system and surroundings is the boundary which determines if energy and mass can be transferred between the system and surroundings An open beaker in which the system is the contents, the boundary surface is the inner wall of the beaker and passes across the open top (exchange freely). A portion of the boundary formed is a wall that can be rigid or movable, permeable or impermeable eg. Balloon surface  The system and surroundings are described on several different variables - Pressure (P) [force/area] - Temperature (T) [determines if system is in thermal equilibrium] - Concentration Ideal Gas Law [1.1] P = pRT - where a dilute gas is under conditions of an ideal gas (p = n/V) [1.2] T = P/pR , for ideal gas systems having same molar density, compare systems and determine if T1 or T2 is greater At the microscopic level, temperature is related to the mean kinetic energy of molecules EQULIBRIUM  Exchangeof energy and matter across a boundary between systems and surroundings is central importance of equilibrium. Thermodynamic equilibrium is the condition in which equilibium exists with respect to one or moreof several different system variables (pressure, temperature and concentration). It is established with respect to a given variable that is UNCHANGED with time and if it is the same temperature in all parts of the system and surroundings Eg. Interior soap bubble (system)and room (surroundings) in equilibrium with respect to P [ the movable wall or bubble can reach a position where P on both sides are the same and has the same value throughout the bubble and room] Equilibrium with respect toconcentration exists only if TRANSPORT OFALL SPECIES ACROSS BOUNDARY IN BOTH DIRECTIONS IS POSSIBLE. Ie. IMPERMEABLE movable wall to some species (if not all) ; equilibrium can exist with P but not with concentration because N2 and O2 cannot diffuse through the (idealized) bubble, the system and surroundings are in equilibrium with P Two systems that have the same temperature (T) are in thermal equilibrium. Consider two systems with rigid walls each having the same molar density equipped with a pressure gauge 1. (n/V)1 = (n/V)2 [T1 (=) T2] T1 not equal to T2 These systems are brought together so that the walls are in intimate contact, pressure is unchanged 2. P1 (=) P2 P1 not equal to P2 (unchanged) * After sufficient time passed, pressures are equal 3. P1 = P2 (changed) so T1 = T2 Walls are DIATHERMAL * Referring to 2, if neither pressure gauge of the systems change , walls are ADIABATIC. The systems are not in thermal equilibrium (T1 (=) T2) since P1 (=) P2 Ie. Coffee in a styrofaoam cup with a lid *Note: experience shows that bringing two systems with adiabatic walls into thermal equilibrium by contact is not possible because the walls are against “heat transfer”. Referring to 3, in bringing the systems into intimate contact, both pressures change and reach same value after some time hence the systems are in thermal equilibrium (T1 = T2 because P1 = P2). The walls are diabatic. Diathermal walls conduct heat so bringing into equilibrium by contact is possible Zeroth Law of Thermodynamics rd Two systems that are separately in thermal equilibrium with a 3 sytem are also in thermal equilibrium with one another. (formulates after 1 law but logically precedes it) We can determine if two systems are in equilibrium without contact. Section 1.3 THERMOMETRY For any useful thermometer, the measured temperature, t, must be a single-valued, continuous and monotonic function of some thermometric system property (ie electric al resistance of a metal/semiconductor and the emf generated at the empirical temperature, t is linearly related to the suction of two dissimilar metals). The value of the thermometric property, x: (1.3) t(x) = a + bx [temperature scale where a is the zero of the scale and b is the size of the unit of the temperature degree] The mercury-in –glass thermometer , the first practical thermometer utilizes the thermometric property that the volume of mercury increases monotonically between -38.8 to 356.7 degrees [Hg]. It was given a standardized scales of values 0 to 100 as signed arbitrarily by Linnaeus in 1745. Because there are 100 degrees between the two calibration points, it is called the centrigrade scale (superceded by Celcius scale). The Celcius scale is determined by one fixed reference point (ice, liquid water and gaseous water in equilibrium) assigned 0.01®C. Boiling point of water is 99.975®C. The size of the degree is chosen to be the same on the centigrade scale. [TRIPLE POINT] - THERMODYNAMIC temperature scale - temperature independent of the substance used in the thermometer and constant a is zero (thermometer, standardized at low temp is where absolute temperature can be measured)  thermometric property is the temperature dependence of P for a dilute gas at constant V [electrical resistanc
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