Concepts
Why can a high-temperature gas be favored even though separating particles requires energy?
At high temperatures, entropy becomes an important consideration for overall "stability". The gas requires a higher potential energy state to separate molecules (unfavorable), but it also achieves more possible configurations (favorable)
Draw a heating curve and label the following:
State of matter
Phase change
Type of energy being absorbed
x = time; y = temp
melting and boiling must be present
solid liquid gas must be present
change in KE during heating
change in PE during phase change
Element X has three naturally occurring isotopes:
50X = 56%
51X = 27%
52X = 17%
Calculate the average relative atomic mass of element X.
50.61 amu
A sample of carbon dioxide gas has a volume of 3.50 L at a pressure of 0.980 atm and a temperature of 45°C. What mass (in grams) of CO2 is present in the container?
5.76 g CO2
A student is given five samples: distilled water, air, copper wire, salt water, and oil + water. Classify each sample as an element, compound, homogenous mixture, or heterogenous mixture.
Distilled water = pure substance + compound
Air = homogenous mixture
Copper wire = elementary substance
Salt water = homogenous mixture
Oil + water = heterogenous mixture
Explain why, during a phase change, the average kinetic energy remains constant even though heat is continuously applied.
Supplied energy is being used to overcome intermolecular attractions (PE) rather than to increase the average KE of the molecules.
Refer to slideshow for graph
a. Rank the liquids from most to least volatile
b. Rank the liquids from strongest to weakest intermolecular interactions
c. If the three liquids are mixed together and separated via distillation at 1 atm, in which order would the liquids be collected?
a. A > B > C
b. C > B > A
c. A, then B, then C
A 240 mL sample of gas is collected at 755 mmHg and 22°C. How many moles of gas are in the sample?
0.00984 mol
If I have 126.09 g of nitrogen, how many grams of hydrogen would I need to form an even amount of ammonia (NH3) without having any atoms left over?
27.216 g H
Identify whether the following gas law relationships are inverse or proportional:
a. Pressure vs. volume
b. Temperature vs. volume
c. Pressure vs. temperature
d. Volume vs. number of moles
a. Inverse
b. Proportional
c. Proportional
d. Proportional
How many neutrons and electrons does a neutral sulfur-34 atom contain?
18 neutrons and 16 electrons
Refer to slideshow for graph
Using claim, evidence, and reasoning (CER), explain which gas sample has the highest temperature.
Claim - curve C represents the gas at the highest temperature
Evidence - the peak of curve C is shifted the furthest to the right, indicating a greater proportion of molecules traveling at higher speeds
Reasoning - temperature is directly proportional to the average kinetic energy of gas particles
How many carbon atoms are in 0.675 mol of acetone (C3H6O)?
An element has two naturally occurring isotopes with masses of 64 amu and 66 amu. Its average atomic mass if 64.60 amu. What is the relative abundance of each isotope?
64 amu = 70%
66 amu = 30%
Explain the significance of the slope of the solid-liquid transition line on a phase diagram.
Positive slopes indicate the solid is denser than the liquid (true for most materials)
Negative slopes indicate the liquid is denser than the solid (true for water)
Two containers of the sample volume hold the same gas at the same initial temperature. Container A has 100 molecules, while container B has 200.
a. Which initially has the greater pressure?
b. How would their pressures' compare if the temperature of container B was halved?
a. B has twice the pressure
b. A and B would have the same pressure (B has twice the molecules but half the temperature)
Refer to slideshow for graph
Two students disagree about which point on the potential-energy curve represents the most stable arrangement of particles.
Student A claims that the particles are most stable at point B, where potential energy is the lowest.
Student B claims that the particles are most stable at point C, where they are the farthest apart.
Using claim, evidence, and reasoning (CER), determine which student's claim is supported by the graph.
Claim - student A's claim is supported by the graph
Evidence - point B is located at the minimum of the potential energy curve, while point C has a higher potential energy (closer to 0)
Reasoning - attractive and repulsive forces are balanced at the minimum of the curve. Moving particles closer together or farther apart requires energy, so point B is the most stable arrangement.
No periodic table:
C5H7O2Br2 has a molar mass of 258.906 g/mol. The atomic masses of the individual elements are:
C = 12.01 amu
O = 16.00 amu
H = 1.008 amu
What is the atomic mass of bromine?
79.9 amu
A 5.00 g sample of an unknown gas occupies 3.00 L at 27.0°C and 101.3 kPa. Determine the approximate molar mass of the sample.
41.1 g/mol
Element "X" has two naturally occurring isotopes, 10X and 11X. 10X forms approximately 70% of natural isotopes, while 11X forms 30%. Element X also forms diatomic molecules (X2).
Identify the possible m/z ratios for the different molecular ion peaks of element X, as well as which peak would be the most abundant.
10X + 10X peak at m/z = 20 (most abundant)
10X + 11X peak at m/z = 21
11X + 11X peak at m/z = 22 (least abundant)
Two hypothetical substances have potential energy curves with a minima at approximately the same inter particle distance. Substance X has a minimum of -20 kJ/mol, while substance Y has a minimum of -50 kJ/mol.
Determine which substance has stronger intermolecular attractions, and why.
Substance Y
The deeper the potential energy well, the more energy require to separate interacting particles. Substance Y requires more energy to separate its particles, indicating stronger attractive interactions.
Samples of helium (He), nitrogen (N2), and xenon (Xe) are all at 300 K.
a. rank their average kinetic energies
b. rank their average molecules speeds
c. sketch a Maxwell-Boltzmann graph with an approximate distribution for each graph
a. All have the same average kinetic energy
b. He > N2 > Xe
c. He is broadest and furthest to the right; N2 is intermediate; Xe is narrow and furthest to the left
A student has a 36.0 g sample of glucose (C6H12O6). How many total atoms are present in the sample?
2.888 x 1024 total atoms
An unknown compound contains 54.5% carbon, 9.1% hydrogen, and 36.4% oxygen. Its molecular ion peak appears at m/z = 88.
Determine the empirical and molecular formula of this compound.
EF = C2H4O
MF = C4H8O2
What is everyone going to get on this exam?
100% !!!!!