AP Chem Test Review
The *standard measurements* for pressure, temperature, volume, and moles.
Pressure: 1 atm = 760 mmHg = 760 Torr = 101.3 kpa = 14.7 PSI = 1.013x10^5 Pa Temperature: 0.00 C = 273.15 K Volume: 22.4 L Moles: 1.00 mol
Ideal Gas Law Equation
PV=nRT
*Root Mean Speed*
Average velocity of gas particles
b
(L/mol)
a
(L^2*atm/mol^2)
For a gas to be ideal, it occurs when there is _________ pressure and ____________ temperature.
*Low Pressure, High Temperature*
For Root Mean Speed and Most probable formula always use ...
- Molar Mass must be *kg* - R units always 8.314 kpa * L/mol * L
Why Ideal gases don't exist?
- Molecules do take up space - All matter has volume - There are attractive forces - Otherwise there would b no liquids
If *Real Gases* behave like Ideal Gases when....
- When molecules are *far apart* - They take a smaller percentage of the space - Ignoring their volume is reasonable - This is at *low pressure* - When molecules are *moving fast* - Molecules are not next to each other very long - Attractive forces can't play a role - At *high temperature* - Far above boiling point
*Coldest possible temperature*
-273 C
*What 6 postulates makes a gas behave ideally?*
1. Gases are composed of a large number of particles that behave like hard, spherical objects in a *state of constant, random motion*. 2. These particles move in a *straight line* until they *collide* with another particle or the walls of the container. 3. These particles are much *smaller* than the distance between particles. Most of the volume of a gas is therefore *empty space*. 4. These is *no force of attraction* between gas particles or between the particles and the walls of the container. 5. Collisions between gas particles or collisions with the walls of the container are perfectly *elastic* (which means NO energy is lost!) 6. The average kinetic energy of a collection of gas particles depends on the *temperature* of the gas and nothing else.
The constant R units
62.4 mmHg * L/mol * K
A sample of oxygen gas was found to effuse at a rate equal to two times that of an unknown gas. The molecular weight of the unknown gas is __________ g/mol. A) 128 B) 8.0 C) 8 D) 16 E) 64
A
The Mond process produces pure nickel metal via the thermal decomposition of nickel tetracarbonyl: Ni(CO)4 (l) ¬ Ni (s) + 4CO (g). What volume (L) of CO is formed from the complete decomposition of 444 g of Ni(CO)4 at 752 torr and 22 C? A) 255 B) 20.2 C) 63.7 D) 11.0 E) 0.356
A
The volume of a sample of gas (2.49 g) was 752 mL at 1.98 atm and 62 C. The gas is __________. A) NO2 B) SO3 C) SO2 D) Ne E) NH3
A
Zinc reacts with aqueous sulfuric acid to form hydrogen gas: Zn (s) + H2SO4 (aq) ¬ ZnSO4 (aq) + H2 (g) In an experiment, 201 mL of wet H2 is collected over water at 27 C and a barometric pressure of 733 torr. The vapor pressure of water at 27 C is 26.74 torr. The partial pressure of hydrogen in this experiment is ________ atm. A) 0.929 B) 760 C) 706 D) 1.00 E) 0.964
A
manometer
A device used to measure the difference in pressure between atmospheric pressure and that of a gas in a vessel.
*Boyle's Law*
A principle that describes the relationship between the pressure and volume of a gas at constant temperature. - As one goes up the other goes down. (inverse relationship)
*Charles's Law*
A principle that describes the relationship between the temperature and volume of a gas at constant pressure. - The volume of a gas is *directly proportional* to the Kelvin temperature if the pressure is held constant.
*effusion*
A process by which gas particles pass through a tiny opening.
Barometer
An instrument that measures atmospheric pressure
According to kinetic-molecular theory, in which of the following gases will the root-mean-square speed of the molecules be the highest at 200 C? A) SF6 B) H2O C) HCl D) Cl2 E) None. The molecules of all gases have the same root-mean-square speed at any given temperature.
B
At 333 K, which of the pairs of gases below would have the most nearly identical rates of effusion? A) CO and CO2 B) CO and N2 C) NO2 and N2O4 D) N2O and NO2 E) N2 and O2
B
SO2 (5.0 g) and CO2 (5.0 g) are placed in a 750 mL container at 50 C. The partial pressure of SO2 in the container was __________ atm. A) 1.60 B) 2.76 C) 4.02 D) 0.192 E) 6.78
B
The density of N2O at 1.53 atm and 45.2 C is __________ g/L. A) 0.388 B) 2.58 C) 9.99 D) 1.76 E) 18.2
B
A sample of a gas (5.0 mol) at 1.0 atm is expanded at constant temperature from 10 L to 15 L. The final pressure is __________ atm. A) 1.5 B) 15 C) 0.67 D) 3.3 E) 7.5
C
Arrange the following gases in order of increasing average molecular speed at 25 C. Cl2, O2, F2, N2 A) Cl2 < O2 < F2 < N2 B) N2 < F2 < Cl2 < O2 C) Cl2 < F2 < O2 < N2 D) F2 < O2 < N2 < Cl2 E) Cl2 < F2 < N2 < O2
C
A sample of He gas (2.35 mol) occupies 57.9 L at 300.0 K and 1.00 atm. The volume of this sample is __________ L at 423 K and 1.00 atm. A) 0.709 B) 57.9 C) 41.1 D) 81.6 E) 1.41
D
The pressure in a 12.2 L vessel that contains 2.34 g of carbon dioxide, 1.73 g of sulfur dioxide, and 3.33 g of argon, all at 42eC is __________ mmHg. A) 116 B) 395 C) 134 D) 263 E) 0.347
D
What volume (mL) of sulfur dioxide can be produced by the complete reaction of 3.82 g of calcium sulfite with excess HCl (aq), when the final SO2 pressure is 827 torr at 44eC? A) 1.39 x 10^-4 B) 0.106 C) 1.00 x 10^-3 D) 761 E) 578
D
A sample of He gas (3.0 L) at 5.6 atm and 25 C was combined with 4.5 L of Ne gas at 3.6 atm and 25 C at constant temperature in a 9.0 L flask. The total pressure in the flask was __________ atm. Assume the initial pressure in the flask was 0.00 atm. A) 24 B) 2.6 C) 9.2 D) 1.0 E) 3.7
E
Sodium hydride reacts with excess water to produce aqueous sodium hydroxide and hydrogen gas: NaH (s) + H2O (l) ¬ NaOH (aq) + H2 (g) A sample of NaH weighing __________ g will produce 982 mL of gas at 28 C and 765 torr, when the hydrogen is collected over water. The vapor pressure of water at this temperature is 28 torr. A) 0.960 B) 925 C) 0.0388 D) 2.93 E) 0.925
E
Pressure
How much *force* is put on the walls of the container from collisions.
What is the *kinetic molecular theory*? (KMT)
Kinetic Molecular Theory is the basis for most gas law calculations and equations.
*Diffusion*
Movement of molecules from an area of higher concentration to an area of lower concentration.
*Joule (J)*
SI unit of energy
*Lussac's Law*
The temperature and pressure are *directly proportional* at constant volume.
What is true about gases at the same temperature?
They have the *same kinetic energy*. If a very massive molecule and a very light molecule have the same kinetic energy, the massive molecule will have a very low velocity while the light molecule will have a high velocity.
*Most probable formula*
U(mp) = (2RT/M)^1/2
What is a means in Van der Waal's equation?
a is a number that depends on how much the molecules stick to each other.
*van der Waals equation*
a mathematical expression for describing the behavior of real gases
What is b means in Van der Waal's equation?
b is a number that determined by how big the molecules are.
*Combination Gas Law*
makes use of the relationships shared by pressure, volume, and temperature, found in other gas laws, such as Boyle's law, Charles' law and Gay-Lussac's law. - P1V1T2 = P2V2T1
*More important formulas*
n = M/MM D = g/L MM = DRT/P D = (MM)P/RT V = nRT/P P = nRT/V M = (MM)PV/RT R = PV/nT n = PV/RT T = PV/nR Molar = mol/L
*Dalton's Law of Partial Pressures*
states that the total pressure of a mixture of gases is equal to the sum of the pressures of all the gases in the mixture.
Avogardo's Law
the law that states that equal volumes of gases at the same temperature and pressure contain equal numbers of molecules.
*mole fraction*
the number of moles of a particular substance expressed as a fraction of the total number of moles.
Graham's Law of Diffusion and Effusion
the rates of diffusion and effusion are inversely proportional to the square roots of their molar masses at the same temperature and pressure. - Kinetic energy = 1/2 mv^2 Bigger molecules move slower at the same temperature (by Square root) - Time 2/Time 1 = (M2)^1/2/(M1)^1/2