Name_______Answers_____________________ Chemistry 121: Test #2
September 14, 2007 8:00 am
READ EACH PROBLEM CAREFULLY. For each of the problems below, you need to SHOW
YOUR WORK and USE UNITS. Full credit will not be given for answers without work, for
numbers without units, or for answers not having the correct number of significant figures.
Useful information
Avogadro’s number = 6.022 x 1023 /mol 1000 g = 1 kg
T (K) = T(°C) + 273.15 1 atm = 101.3 kPa = 760 mmHg
Molarity, M = (mol solute)/(L solution) R=0.0821 atm L / (mole °K)
Cp, H2O = 4.184 J/g°C Density of water = 1.00 g/mL
q = mCp∆T ∆H = [∆Hproducts] – [∆Hreactants]
χA = nA/ntotal P
A = χAPtotal
1. (5 pts)What does “STP” stand for? What are the values of temperature and pressure at STP ?
Standard Temperature and Pressure 273 K (0 °C) and 1 atm
2. (6 pts) Assume you have a balloon which contains a sample of an ideal gas. What would
happen to the gas pressure when you do each of the following? (assume other gas variable
remain constant)
a. reduce the temperature to half its original value
the pressure will decrease by half
b. increase the volume of gas to double the original value
the pressure will decrease by half
3. (10 pts) A neon sign is made of glass tubing shaped to spell the phrase “Chemistry is Fun”.
The total volume of the tubing is 8.0 L. If the sign contains neon at a pressure of 2.03 mmHg at
35 °C, how many grams of neon are in the sign ?
V= 8.0 L n=PV/(RT)=(0.00267)(8.0)/(0.0821*308)
P= 2.03 mmHg x (1atm/760mmHg) = 8.5 x 10-4 moles Ne
= 0.00267 atm
T= 35+273.15 = 308 K mass = 8.5 x 10-4 moles Ne * (20.18 g Ne/1moleNe)
= 0.017 g Ne
4. (10 pts) A gas bubble with a volume of 1.00 mL originates from under the fin of a fish at the
bottom of a lake where the pressure is 3.0 atm. Calculate the bubble’s volume (in mL) when it
reaches the surface of the lake where the pressure is 0.914 atm. Assume that the gas temperature
does not change.
V1= 1.00 mL = 0.00100 L P1V1 = P2V2
P
1= 3.0 atm (3.0)(0.00100) = (0.914)V2
P
2= 0.914 atm V2= 0.0033 L = 3.3 mL
