ERT 108 Physical Chemistry INTRODUCTION-Part 2 by Mdm Rohazita Bahari

Thermodynamic- Basic concepts (cont.) Equilibrium: Variable (eg: pressure, temperature, & concentration) does not change with time Has the same value in all parts of the system and surroundings. Thermal equilibrium: No change of temperature occurs when two objects A and B are in contact through a diathermic boundary (thermally conducting wall). Mechanical equilibrium: No change of pressure occurs when two objects A and B are in contact through a movable wall.

THERMODYNAMIC EQUILIBRIUM A system is said to be thermodynamic equilibrium when it is in thermal equilibrium and mechanical equilibrium and chemical equilibrium. Thermal equilibrium equality of temperature Mechanical equilibrium equality of force pressure Chemical equilibrium there must be have equal chemical potential

Example: Thermal Equilibrium Wall is diathermal Both pressures change. Reach the same value after some time. In thermal equilibrium (T1=T2)

Not in thermal equilibrium Example Wall is adiabatic No pressure change. P1≠ P2. Not in thermal equilibrium

Thermal equilibrium Video 1

Thermodynamic- Basic concepts (cont.) Zeroth Law of thermodynamics: Two systems that are each found to be in thermal equilibrium with a third system will be found to be in thermal equilibrium with each other. If A is in thermal equilibrium with B, and B is in thermal equilibrium with C Then, C is also in thermal equilibrium with A. A Thermal equilibrium Thermal equilibrium Thermal equilibrium B C

ZEROTH LAW OF THERMODYNAMIC Video 2

Mechanical equilibrium When a region of high pressure is separated from a region of low pressure by a movable wall, the wall will be pushed into one region or the other: There will come a stage when two pressures are equal and the wall has no tendency to move. Movable wall High pressure Low pressure Low pressure High pressure In mechanical equilibrium (P1=P2) Equal pressure Equal pressure

The greater the force acting on a given area, the greater the pressure P= pressure, Pa F= Force, N A=Area, m2

Video 3

Exercise: 1) A force of 15Newtons is applied over an surface area of 0.6m2. What is the pressure?. 2) A 20lb box with a length of 10 inches and a width of 5 inches is resting on the floor. How much pressure does if exert on the floor?. 3) A box has a weight of 20lbs and exerts a pressure of 0.5psi, what is the area?.

Exercise: 4) Calculate the pressure exerted by a mass of 1.0 kg pressing through the point of a pin of area 1.0 x 10-2 mm2at the surface of the Earth. The force exerted by a mass m due to gravity at the surface of the Earth is mg, where g is the acceleration of free fall.

Solution: Calculate the pressure exerted by a mass of 1.0 kg pressing through the point of a pin of area 1.0 x 10-2 mm2at the surface of the Earth. The force exerted by a mass m due to gravity at the surface of the Earth is mg, where g is the acceleration of free fall.

GAS LAWS Boyle’s Law Charles’s Law Avogadro’s Principle Stating that the pressure and volume of a gas have an inverse relationship, when temperature is held constant. Charles’s Law Is an experimental gas law that describes how gases tend to expand when heated. When the pressure on a sample of a dry gas is held constant, the kelvin temperature and the volume will be directly related. Avogadro’s Principle Equal volumes of all gases, at the same temperature and pressure, have the same number of molecules.

Boyle’s Law Video 5a & 5

P and V are inversely proportional. Gas laws Boyle’s law at constant mass and temperature A decrease in volume causes the molecules to hit the wall more often, thereby increasing the pressure. is a constant P and V are inversely proportional.

Charle’s Law Video 6a & 6

P and T are directly proportional. Gas laws P and T are directly proportional. Charle’s law at constant mass and pressure at constant mass and volume constant

Avogadro’s principle Video 7a & 7

Gas laws Avogadro’s principle; at constant pressure and temperature Equal volumes of gases at the same temperature and pressure contain the same numbers of molecules. at constant pressure and temperature

Exercise: Boyle’s + Charle’s and Avogadro’s principle.

Ideal Gas Law Combination of 3 related laws that were discovered by variety of scientists. Boyles’s Law : PV = nRT = k *(if n, T = constant) Charle’s Law : V/T = nR/P = b *(if n, P = constant) Avogadro’s Law : V/n = RT/P = a * (if T, P = constant)

Boyles’s Law : P1VI = P2V2 *(if n, T = constant) Charle’s Law : V1/T1 = V2/T2 *(if n, P = constant) Avogadro’s Law : V1/n1 = V2/n2 * (if T, P = constant)

PV = nRT Ideal Gas Law Temp of gas in Kelvin Pressure in atm moles of gas Volume of gas in liters Universal gas Law constant R= 0.0821 L.atm/mol.K

Ideal Gas Ideal gas is a gas that obeys ideal gas law: Ideal gas law Gas Constant

Value R The Universal Gas Constant, value R depends on unit of Pressure R = 8.3145 L. kPA/K. mol R = 0.0821 L. atm/ K.mol R = 62.4 L.mmHg/K.mol

PRESSURE Pressure = Force/Area P = F/A 1 Pa = 1N/m2

ATM 1 ATM 1atm = 101325 Pa ~ 100kPa

Standard Temperature and Pressure (STP) STP is a standard set of conditions for experimental measurement established to allow comparisons to be made between different sets of data STP 273K 1 atm (remember: STP, the temp. will always 273K and pressure will always 1 atm)

1 mole of any ideal gas takes up 22.4 Liters of space at STP Zero degree 100,000 pascals = 100 kilopascals 1 mole of any ideal gas takes up 22.4 Liters of space at STP

Temperature at which all movement of all particles stops ABSOLUTE ZERO Temperature at which all movement of all particles stops 0 Kelvins = -273.15 deg

Example: laws At the temperature of 45 deg and pressure of 250kPa. How many moles will fill a container that is 16L in volume? (hint : changes before n after ?) 2) A sample of gas taken u 45L. After being compresses down to a volume of 12L. The sample has a pressure of 5.7 atm. What was the original pressure? (hint : temperature constant) 3) A temperature of 65 deg & a pressure of 1,120 mmHg, a large balloon takes up 25L. What the volume become if the temperature is lowered to 5 deg? (hint : assume pressure constant)

4) at 1. 70 atm, a sample of gas takes up 4. 25L 4) at 1.70 atm, a sample of gas takes up 4.25L. If the pressure on the gas is increased to 2.40 atm, What will the new volume to be? (hint : temperature constant) 5) A balloon takes up 625L at 0 deg. If it is heated to 80 deg, what will its new volume? (hint : pressure constant) 6) In a sample of gas, 50.0g of Oxygen gas (O2) take up 48L of volume. Keeping the pressure constant, the amount of gas is changed with the volume is 79L. How many grams of gas are now in the container? (hint : O = 16g/mol )

Examples: ideal gas law Ten liters of a gas exerts 2.5 atm of pressure at 200K. How many moles of gas are there? We will assume the gas behave ideally. (hint: given V, P, T and n=?) PV=nRT 2) If 64 grams of oxygen gas (O2) at 350K exerts 1,520 torr of pressure then what is its volume? We will assume the gas behaves ideally. (hint: n= grams change to mol ;molecular weight O2=32g), P=change to atm,; 1 torr = 0.00132atm, V=?)

Examples: 3) Six moles of a gas occupies 20L at a pressure of 2.8 atm. What is the gas temperature? Assume the gas behaves ideally. (hint: given, n, V, P and T=?) 4) Haw much space does 1 mol of gas occupy at STP? Assume the gas behaves ideally. (hint: STP, K &atm state) *molar volume of a gas at STP

Exercise In industrial process, nitrogen is heated to 500 K in a vessel of constant volume. If it enters the vessel at 100 atm and 300 K, what pressure would it exert at the working temperature if it behaved as an ideal gas?

Ideal Gas Mixture Dalton’s law: Ideal gas mixture The pressure exerted by a mixture of gases is the sum of the pressure that each one would exert if it occupied the container alone. Ideal gas mixture

Partial pressure, Pi of gas i in a gas mixture: Where For an ideal gas mixture: any gas mixture

Exercise The mass percentage composition of dry air at sea level is approximately N2= 75.5, O2=23.2, Ar= 1.3 What is the partial pressure of each component when the total pressure is 1.20 atm?

Real gas Real gas do not obey ideal gas law except in the limit of p0 (where the intermolecular forces can be neligible) Why real gases deviate from ideal gas law? Because molecules interact with one another. (there are attractive and repulsive forces)

Real gas- molecular interaction At low P, when the sample occupies at large volume, the molecules are so apart for most time that the intermolecular forces play no significant role, and behaves virtually perfectly/ideally. At moderate P, when the average separation of the molecules is only a few molecular diameters, the ATTRACTIVE force dominate the repulsive forces. The gas can be expected to be more compressible than a perfect gas because the forces help to draw the molecules together.

Real gas- molecular interaction At high pressure, when the average separation of molecules is small, the repulsive force dominate, and the gas can be expected to be less compressible because now the forces help to drive molecules apart.

Real gas Compression factor, Z At very low pressures, Z ≈ 1 The extent of deviation from ideal gas behaviour is calculate using compression factor, Z At very low pressures, Z ≈ 1 At high pressures, Z>1 At intermediate pressure, Z<1

Real gas equations Virial equation of state: van der Waals equation: Compression factor, Z