REGENTS CHEMISTRY LETS REVIEW>>>>>> whispers from the past

Two hydrogen atoms form a hydrogen molecule when REGENTS QUESTION Two hydrogen atoms form a hydrogen molecule when (1) one atom loses a valence electron to the other atom (2) one atom shares four electrons with the other atom (3) the two atoms collide and both atoms gain energy (4) the two atoms collide with sufficient energy to form a bond

Which unit is used to express the pressure of a gas? (1) mole REGENTS QUESTION Which unit is used to express the pressure of a gas? (1) mole (2) kelvin (3) joule (4) pascal

REGENTS QUESTION Which sample of matter sublimes at room temperature and standard pressure? (1) Br2(ℓ) (2) CO2(s) (3) Cl2(g) (4) SO2(aq)

REGENTS QUESTION Given the balanced equation representing a reaction: H2 + energy → H+H What occurs as bonds are broken in one mole of H2 molecules during this reaction? (1) Energy is absorbed and one mole of unbonded hydrogen atoms is produced. (2) Energy is absorbed and two moles of unbonded hydrogen atoms are produced. (3) Energy is released and one mole of unbonded hydrogen atoms is produced. (4) Energy is released and two moles of unbonded hydrogen atoms are produced.

Properties of Gases (Review) No definite shape No definite volume compressible

The Behavior of Gases

Entropy is a measure of the (1) acidity of a sample REGENTS QUESTION Entropy is a measure of the (1) acidity of a sample (2) disorder of a system (3) concentration of a solution (4) chemical activity of an element

Which element is a gas at STP? (1) sulfur (2) potassium REGENTS QUESTION Which element is a gas at STP? (1) sulfur (2) potassium (3) xenon (4) phosphorus

Which element is least likely to undergo a chemical reaction? REGENTS QUESTION Which element is least likely to undergo a chemical reaction? (1) lithium (2) fluorine (3) carbon (4) neon

Kinetic Molecular Theory moving molecules well supported ideas

Basic Kinetic Theory of Gases Composed of particles like atoms (ex: He) or molecules like (O2 and CO2) There are no attractive/repulsive forces. Lots of empty space!!

Basic Kinetic Theory of Gases 2. Particles move in random, constant, straight-line motion. Move independently of each other.

Basic Kinetic Theory of Gases 3. All collisions are elastic meaning that KE is transferred without loss of energy. No change in kinetic energy. Gases tend to diffuse towards areas of lower concentration.

REGENTS QUESTION According to the kinetic molecular theory, which statement describes the particles of an ideal gas? (1) The gas particles are arranged in a regular pattern. (2) The force of attraction between the gas particles is strong. (3) The gas particles are hard spheres in continuous circular motion. (4) The collisions of the gas particles may result in the transfer of energy

REGENTS QUESTION: Which statement describes particles of an ideal gas, based on the kinetic molecular theory? (1) Gas particles are separated by distances smaller than the size of the gas particles. (2) Gas particles do not transfer energy to each other when they collide. (3) Gas particles have no attractive forces between them. (4) Gas particles move in predictable, circular motion.

What is the gram formula mass of H2O? H 2 X 1= 2 O 1 X 16= 16 MENTAL PIT STOP formula mass What is the gram formula mass of H2O? H 2 X 1= 2 O 1 X 16= 16 18 amu or g

What is the gram formula mass of LiF? Li 1 X 7= 7 F 1 X 19= 19 MENTAL PIT STOP What is the gram formula mass of LiF? Li 1 X 7= 7 F 1 X 19= 19 26 amu or g

Gas Pressure Pressure- force exerted on container walls by particles in a gas Units used- kPa, atm, Torr, mmHg STP (Standard Temperature and Pressure) Table A 273 K or 0°C and 101.3 kPa = 1 atm = 760 Torr (mmHg)

Factors Affecting Pressure Amount of Gas (number of moles) Increasing amount will increase P (and vice versa) Ex: bicycle tires, car tires Temperature Increasing temp. will increase P (and vice versa) Ex: Tires deflate in winter Volume Decreasing volume will increase P, increasing volume decreases P Ex: press down on a balloon and it pops

P1V1=P2V2 Pressure and volume have an inverse relationship, if temperature remains constant. If volume is increased, pressure is decreased by the same factor.

Mathematically, the product of PV is constant or PV = k (where k is some constant). Boyle’ Law P1 V1 = P2 V2 = P3 V3…

Summary

GRAPH #1 REGENTS QUESTION A rigid cylinder with a movable piston contains a sample of helium gas. The temperature of the gas is held constant as the piston is pulled outward. Which graph represents the relationship between the volume of the gas and the pressure of the gas? GRAPH #1

Given the balanced equation representing a reaction: MENTAL PIT STOP Given the balanced equation representing a reaction: 2NO + O2 → 2NO2 + energy The mole ratio of NO to NO2 is 1 to 1 (2) 3 to 2 (3 ) 2 to 2 (4) 5 to 2

Determine the percent composition by mass of oxygen in the CaCO3. MENTAL PIT STOP Determine the percent composition by mass of oxygen in the CaCO3. Ca 1 X 40= 40 C 1 X 12=12 O 3 X 16 =48 48/100 X 100% = 48 %

Volume vs. Temperature V1/T1 =V2/T2 Volume and temperature have a direct relationship, if pressure is held constant. If temperature (K) is increased, volume is increased by the same factor.

Mathematically, the relationship of volume divided by Kelvin temperature is constant or V/T = k. Charles’ Law V1 /T1 = V2 /T2 = V3 /T3 …

Summary

Pressure vs. Temperature P1/T1 =P2/T2 Pressure and temperature have a direct relationship, if volume remains constant. If temperature (K) is increased, pressure will be increased by the same factor.

Mathematically, the relationship of volume divided by Kelvin temperature is constant or P/T = k. Gay-Lussac’s Law P1 /T1 = P2 /T2 = P3 /T3 … Pressure

Pressure/Temperature relationship Pressure increases, Temp. increases

Combined Gas Law Equation P1 V1 = P2 V2 T1 T2

Which sample of matter is a mixture? MENTAL PIT STOP Which sample of matter is a mixture? (1) Br2(ℓ) (2) KBr(s) (3) K(s) (4) KBr(aq)

MENTAL PIT STOP According to kinetic molecular theory, collisions between gas particles in a sample of an ideal gas (1) increase the energy content of the gas sample (2) produce strong attractive forces between the gas particles (3) result in a net loss of energy by the gas sample (4) transfer energy between the gas particles

Combined Gas Law Equation Steps: Determine which variable (if any) is kept constant. Cancel those terms and remove them from the equation (Ex: If the question says that temperature remains constant the new equation becomes P1V1 = P2V2). Plug in values that are given. Solve for the unknown. Be sure to always use temperature in Kelvins.

Ideal Gases vs. Real Gases “Ideal gases” behave as predicted by Kinetic Molecular Theory. Examples: H2 and He Gases are most ideal at high temperature and low pressure (also have low mass and low polarity).

“Real gases” deviate from ideal behavior. Why? At low temps, gas particles become attracted to each other (KMT says they are not). Under high pressure, gases occupy a specific volume (KMT says they don’t).

(1) low pressure and low temperature REGENTS QUESTION A sample of hydrogen gas will behave most like an ideal gas under the conditions of (1) low pressure and low temperature (2) low pressure and high temperature (3) high pressure and low temperature (4) high pressure and high temperature

Avogadro’s Law Avogadro’s number: 6.02 x 1023 Simply refers to the quantity of particles found in a mole. At STP, 6.02 x 1023 particles of a gas occupies 22.4 L. At STP, 3.01 x 1023 particles of a gas occupies 11.2 L.

Avogadro’s Law Avogadro also hypothesized that equal volumes of different gases at the same temperature and pressure contain equal number of particles (or equal moles).

REGENTS QUESTION 6/2013 #60-62 Cylinder A has a movable piston and contains hydrogen gas. An identical cylinder, B, contains methane gas. The diagram below represents these cylinders and the conditions of pressure, volume, and temperature of the gas in each cylinder. *

*Compare the total number of gas molecules in cylinder A to the total number of gas molecules in cylinder B. [1] same volume means same number of molecules State a change in temperature and a change in pressure that will cause the gas in cylinder A to behave more like an ideal gas. [1] high temperature low pressure *In the space in your answer booklet, show a numerical setup for calculating the volume of the gas in cylinder B at STP. [1] (1.2) ( 1.25) = (1) (x) 293 273

MENTAL PIT STOP Under which conditions of temperature and pressure does a real gas behave most like an ideal gas? (1) 37 K and 1 atm (2) 347 K and 1 atm (3) 37 K and 8 atm (4) 347 K and 8 atm

MENTAL PIT STOP The diagram and data below represent a gas and the conditions of pressure, volume, and temperature of the gas in a rigid cylinder with a moveable piston. Determine the volume of the gas in the cylinder at STP. (1) (2.5) = (1) (x) 298 273 State one change in temperature and one change in pressure that will cause the gas in the cylinder to behave more like an ideal gas. Temp higher than 298 K, Pressure lower than 1.0 atm

Vapor Pressure In a sealed container, vapor pressure can be measured above a liquid. Evaporation occurs when some particles from the surface of a liquid escape causing pressure to build up above the liquid (not to be confused with boiling).

Vapor pressure illustrated

Factors that Increase the Rate of Evaporation Heating a liquid (not to boiling point) Increasing surface area Create air currents (blow across the surface)

Liquid-Vapor Equilibrium Some of the gas particles condense and then we find both evaporating and condensing occurs at the same rate. Rate of Evaporation = Rate of Condensation

Related to Boiling Boiling occurs when the vapor pressure becomes equal to the external pressure. At normal atmospheric pressure, we call this normal boiling point.

Boiling and Attractive (Intermolecular Forces) Boiling occurs when heat energy overcomes attractive forces between molecules. The stronger the intermolecular forces, the higher the boiling point. The weaker the intermolecular forces, the lower the boiling point.

Table H Notice, increasing temperature increases vapor pressure. Line drawn at 101.3 kPa corresponds to normal boiling point.

REGENTS QUESTION Rubbing alcohol is a product available at most pharmacies and supermarkets. One rubbing alcohol solution contains 2-propanol and water. The boiling point of 2-propanol is 82.3°C at standard pressure. Determine the vapor pressure of water at a temperature equal to the boiling point of the 2- propanol. [1] >  Table H...a pressure between 48kPa and 52kPa