NYS Unit 4 Questions on Phys Behav of Matter

DC Chem Gases Unit Test. Chemistry/CCS/Dr.Zisk NAME______NB: The Universal Gas Constant “R” is 8.2 x 10-2 L·atm/K·mol or 8.3 L·kPa/K·mol…

1. Real gases will behave most like ideal gases when the gas sample is at relatively (1) high temperature and high pressure (2) high pressure and low temperature (3) high temperature and low pressure (4) low temperature and low pressure

2. An ideal gas in a 5 L balloon is brought from 273 K to 0.273 K at constant pressure. Its new volume must be: (1) 500 L (2) 1 L (3) 0.5 L (4) 0.005 L

3. The volume of a gas is 4.00 liters at 293 K and constant pressure. For the volume of the gas to become 3.00 liters, the Kelvin temperature must be equal to: (1) (3.00x293)/4.00 (2) (4.00/293)x3.00 (3) 293/(4.00x3.00) (4) (293x4.00)/3.00

4. When a gas balloon is brought to a new pressure that is 1/4 of the previous surroundings, with no change in temperature, what must the new volume be? (1) 4 times the old volume (2) there is no change (3) 1/4 of the old volume (4) 1/16 of the old volume

5. A sample of helium gas has a volume of 900. milliliters and a pressure of 2.50 atm at 596 K. What is the new pressure when the temperature is changed to 298 K and the volume is decreased to 450. milliliters? (1) 5.0 atm (2) 1.25 atm (3) 2.50 atm (4) 1.0 atm

6. Which graph best represents the pressure volume relationship for an ideal gas at constant temperature?

…the answer is (4)

7. Real gases that behave least like ideal gases are similar to (1) ping pong balls on a trampoline (2) magnetic bowling balls in a cast iron bathtub (3) dust in the wind (4) firework

8. Realistic Problem: A weather balloon containing 20.0 L of He, at 23 C and 100 kPa, rises to a height where pressure drops to 10 kPa and temperature drops to –74.1 C. Calculate the new volume in the steps below. NOTE— All units for full credit!

a. give the equation: (PV/T)1 = (PV/T)2

b. show your substitutions: (100kPa)(20.0L)/296K = (10kPa)(V2)/198.9K

c. calculate an answer. Answer: _( 198.9K)(100kPa)(20.0L)/(296K)(10kPa) = (V2 ) = ___ 100L

9. A sample of 224.0 L of CO2 gas, an IG@STP, is how many moles of the molecule? Answer: _22.4L=1mole so 224L= 10 moles

10. How many moles of atoms are there in problem #9? Answer: _@ 3 atoms per molecule, it’s 30 atoms 11. A sample of 880 grams of CO2 is how many moles? Answer: GFM of 44g/mol, so 880g = 20 moles______

12. Give a short phrase or sentence describing the three main ideas of KMT and why each idea makes a gas “ideal”… Idea #1: __no attractions____ How it makes gases ideal: gases take up volume, behave “linearly” not collapsing non-linearly as they get closer Idea #2: __”particles” of gas have no size compared to the distance between them How it makes gases ideal: at small volumes, gas particles don’t interfere with each other; squeeze stays linear Idea #3: _ straight-line motion __ How it makes gases ideal: they behave in a “regular” way-- nothing volitional, arbitrary or unpredictable

13. Realistic Problem: In Mr. Lindridge’s shop, 25 moles of oxygen and 75 moles of acetylene (which has the formuls C2H2) gases are pumped through the nozzle of a welding torch. The pressure where they meet to make the flame comprises a 500 kPa total.

a. What is the mole fraction of each gas? For oxygen, 25 mol out of (25 + 75) is 25%… and hence, 75% acetylene.

b. What are the partial pressures of each gas? For oxygen, 25% of the 500kPa total makes 125kPa partial P of O2… …and then 375kPa of acetylene.

14. How many moles of H atoms is this in Question #13? 75 mol of acetylene, C2H2, at 2 H’s per molecule means 150 mol of H atoms.

15. Two ideal gases: At STP, 4 liters of O2 contains the same total number of molecules as

(1) 1 L of NH3 (2) 8 L of He (3) 2 L of Cl2 (4) 4 L of CO2

16. Prove that 1.00 mole of ideal gas at STP must occupy 22.4 L of volume.

use PV=nRT, substituting… (101.3kPa)(V) = (1mol)(8.3 LkPa/Kmol), solving for V… V= 1.0 mole

17. In your labs the gases failed to behave ideally under certain conditions. For each lab separately—Guy-Lussac’s P vs. T Law and Boyle’s V vs. P Law— what was your clue that the gases weren’t behaving ideally, and why was it happening? a. Guy-Lussac: What did you observe that was non-ideal? at low T, there was condensate, and the V got smaller than expected… b. What did it mean? gas particles were attracted to each other… c. Boyle: What did you observe that was non-ideal? at high P, there was condensate, and the V got smaller than expected… d. What did it mean? gas particles were attracted to each other…