V10 Semester Two Exam Review Key
1. Describe the spacing between particles of a solid, liquid and gas
Solids-molecules packed tightly together
Liquid-molecules closer farther apart than in a solid but closer together than in a gas
Gas-molecules have a lot of empty space between them
2. Describe the shape and volume of a solid, liquid and gas
Solid-Definite shape and volume
Liquid-Indefinite shape and definite volume
Gas-Indefinite shape and volume
3. Describe the energy change that occurs during phase changes. Are these physical or
chemical changes?
Solid to liquid-Molecules vibrate faster and kinetic energy increases. Physical change.
Liquid to gas- Molecules vibrate faster and kinetic energy increases. Physical change.
Gas to Liquid-Molecules vibrate more slowly and kinetic energy decreases. Physical
change.
Liquid to solid- Molecules vibrate more slowly and kinetic energy decreases. Physical
change.
4. A sample of gas has a volume of 4.3 L and a pressure of 2.6 atm. What is the pressure
of the gas if the volume is raised to 3.6 atm?
P1 x V 1 = P2 x V2
(2.6 atm) x (4.3 L) = P2 x (3.6 atm)
11.18 L x atm = P2 x 3.6 atm
(11.18 L x atm) / 3.6 atm = (P2 x 3.6 atm) / 3.6 atm
3.1 L = P2
5. A sample of gas has a volume of 7.70 L and a temperature of 350 K. What is the new
volume if the temperature decreases to 320 K?
V1 / T1 = V2 / T2
7.70 L / 350 K = V2 / 320 K
(7.70 L x 320 K) / 350 K = (V2 x 320 K) / 320 K
2464 K x L / 350 K = V2
7.04 L = V2
6. If 35 g H2 gas occupies a volume at 42 L at a temperature of 20 degrees Celsius, what is
the pressure in atmospheres?
35 g x 1 mol / 2.018 g H2 = 17.34 mol H2
K = 20oC + 273
K = 293
PV = nRT
P (42 L) = (17.34 mol H2) (0.0821 Lxatm/mol x K) (293 K)
P(42 L) = 417.1 L x atm
P(42L) / 42L = (417.1 Lx atm) / 42 L
P = 9.93 atm
7. What are the values for standard temperature and pressure?
Temperature-273.15 K
Pressure – 1 atm
8. If 3.6 L CH4 gas combusts with excess O2 at standard temperature and pressure, how
many L of water vapor are produced?
CH4 + 2O2 -> CO2 + 2H2O
3.6 L CH4 x (2 L H2O/1 CH4) = 7.2 L H2O
9. What are each of the following techniques used to separate?
Filtration-Separates an insoluble solid from a liquid by pouring a liquid through a filter
over a beaker. The liquid flows through the filter into the beaker and the solid stays
behind.
Evaporation-Good for separating a soluble solid from a liquid because the liquid can be
evaporated, leaving the solid behind.
Simple Distillation-Separates a liquid from solution. One liquid is evaporated and
condenses into a separate container and the other liquid is left behind.
Chromatography-Separates polar substances. Paper chromatography is a technique
where a solution is placed near the end of the paper, the paper is placed into a liquid
such as alcohol and the solution on the paper separate into different positions based on
their attraction to the paper (polarity).
10. When 5.3 grams of KCl are dissolved in enough water to create a 122-gram solution,
what is the solution's concentration, expressed as a percent by mass?
(5.3 g solute / 122 g solution) x 100%
0.0434 x 100% = 4.34 % KCl
11. Why is water called the universal solvent?
Many different substances will dissolve in water.
12. What is the definition of surface tension?
A property of liquids, caused by the attraction between molecules, which makes the
surface less penetrable by solid objects.
13. What happens to water molecules as they freeze? What special properties does this
give water?
When water molecules freeze, they move farther apart. This is why ice floats.
14. How many milliliters of a 3.5 molar hydrochloric acid solution would be needed to
react completely with 40.0 grams of magnesium metal?
Mg + 2HCl -> MgCl2 + H2
40.0 g Mg x (1 mol Mg / 24.3050 g Mg) x (2 mol HCl / 1 mol Mg) x (1 L HCl x 3.5 mol HCl)
= 80 L HCl / 85.0675 = 0.94 L HCl
0.94 L x (1 mL / 1 x 10-3 L) = 940 mL HCl
15. How do you find molality of a covalent compound? Of an ionic compound?
Molality = moles of solute (mol) / kilograms of solvent (kg)
For a covalent compound such as C6H12O6, the bonds of the molecule are not broken so
if you have one mole of glucose, the solution will have one mole of solute particles.
For an ionic compound, NaCl is ionic. When NaCl dissolves it breaks into one mole of Na +
and one mole of Cl- giving a total of 2 solute particles.
16. Which of the following is the best example of a closed system?
A juice box with a straw in it
a sealed medicine bottle
an insulated coffee mug
our planet
17. For an endothermic reaction, what would the potential energy diagram most likely
look like?
a curve with a negative slope indicating that the activation energy has a negative value
a curve indicating that the amount of energy absorbed during the reaction is high
a curve indicating that the potential energy of the reactants is higher than the products
a curve indicating that the potential energy of the products is higher than the reactants
18. Which of the following is an example of an endothermic process?
a package of broccoli freezing in a freezer
burning gasoline in a lawn mower
an ice cream sandwich melting on a picnic table
moisture forming on a mirror in the bathroom
19. If you add a 20 gram piece of metal at a temperature of 103° Celsius to a sample of
100 grams of water at 28° Celsius inside a calorimeter, what best describes what will
occur?
The final temperature of the water will be less than 24° Celsius.
The temperature gained by the water will equal the temperature lost by the metal.
The thermal energy lost by the metal will equal the thermal energy gained by the water.
The final temperature of the water will be 95° Celsius.
20. The specific heat of calcium metal is 0.65 J/(g × °C). How much energy must be added
to a 55.0 gram sample of calcium to change the temperature from 20.0°C to 45.0°C?
q= m x c x ΔT
q= (55)(0.65)(25)
894 J
21. 25.5 grams of an unknown substance is heated to 105.0 degrees Celsius and then
placed into a calorimeter containing 100.0 grams of water at 26.0 degrees Celsius. If
the final temperature reached in the calorimeter is 29.5 degrees Celsius, what is the
specific heat of the unknown substance? Show or explain the work needed to solve
this problem, and remember that the specific heat capacity of water is 4.18 J/(°C x g).
q = m x c x ΔT
q surroundings= 100 x 4.18 x (29.5-26.0)
q surroundings= 1463
q surrounds = -q system
-1463 = 25.5 x c x (29.5 – 105.0)
-1463/-1925.25 = c
C= .76
22. Which statement about the following reaction is correct?
CH4 (g) + 2O2 (g) CO2 + 2H2O ΔH = -780 kJ
reacting one mole of oxygen O2 absorbs 390 kJ of energy
reacting one mole of oxygen O2 releases 390 kJ of energy
reacting one mole of methane CH4 absorbs 780 kJ of energy
reacting two moles of methane CH4 releases 780 kJ of energy
23. After a shower you notice water vapor condensed on the mirror. Which of the
following best describes what happens during the condensation process?
increase in enthalpy of the system
increase in kinetic energy
decrease in entropy of the system
decrease in activation energy
24. Which of the following changes would increase the rate of a reaction between vinegar
and baking soda?
diluting the vinegar
cooling the vinegar
heating up the vinegar
decreasing the volume of the container
25. Predict how the addition of iodine gas would affect the initial rate of the reaction
below, and explain your prediction.
H2 (g) + I2 (g)  2 HI
Adding reactant to the system increases the number of collisions and would push it to
the right.
26. Which of the following characteristics is not a property of a base?
has a bitter taste
feels slippery to the touch
reacts with active metals to produce hydrogen gas
increases the concentration of hydroxide ions in an aqueous solution
27. Determine the pH of the following solutions:
[H3O+] = 1 X 10 -6 M
pH = - log [H3O+] = 6,
1
EXP
±
6
log
±
=
6
6
P\\\\
6
6
This is what I type in my calculator:
[OH-] = 1 X 10 -2 M
[H3O+] x [OH-] = 1 X 10 -14 ; then [H3O+] = 1 X 10 -14 / 1 X 10 -2 ;
[H3O+] = 1 X 10 -10 ; then pH = = - log [H3O+] = 10
28. Which of the following is an acid-base neutralization reaction?
Sn + 2HBr
SnBr2 + H2
HCl + KOH
KCl + H2O
2AlCl3 + 3Ca(OH)2
2C2H6 +7O2
2Al(OH)3 + 3CaCl2
4CO2 + 6H2O
29. In a titration, 20.0 milliliters of 1.5 molar NaOH are needed to neutralize 15.0
milliliters of H2SO4, what is the concentration of the H2SO4 solution?
Balanced equation: 2 NaOH + H2SO4
Na2SO4+ 2 H2O
2.0 M H2SO4
0.50 M H2SO4
1.3 M H2SO4
1.0 M H2SO4
Basically you should know n1M1V1=n2M2V2 ; where substance 1 = Na(OH) and substance
2 = H2SO4. Because NaOH, has 1 group OH, while H2SO4 has two groups H, so that is n1
=1, M1 = 1.5 M, V1 = 20 mL and n2=2, M2 = unknown , V2 = 15 mL
So putting the values into the equation n1M1V1=n2M2V2 you get
1 x 1.5 x 20= 2 x M2 x 15 ; M2 = 1.0 M
30. What does it means for a chemical system to be in the state of dynamic equilibrium?
What does the value, or magnitude, of the equilibrium constant (K) tell you about an
equilibrium system?
When a system reaches equilibrium the rates of the forward and reverse reactions are
equal.
After equilibrium the concentration of reactants and products remain constant.
In the equilibrium constant, K, product concentrations appear in the numerator and
reactant concentrations appear in the denominator.
a. K >1  When this system reaches equilibrium there will be more products than
reactants.
b. K <1  When this system reaches equilibrium there will be more reactants than
products.
31. An equilibrium mixture is transferred from a 1 L flask to a 2 L flask. In which direction
does a net reaction proceed to restore equilibrium?
Balanced equation is 2 SO3 (g)
2 SO2 (g) + O2 (g)
http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/lechv17.swf
If V is increased (or system pressure is reduced), the equilibrium shifts in the direction of
producing more moles of gas. In this reaction, when increasing the volume, it would
displace toward the products.
32. For the following reaction, identify the element that was oxidized, the element that
was reduced, and the reducing agent. Give an explanation for each answer.
Balanced equation is: Zn + H2SO4
ZnSO4 + H2
Zn is an element, so its oxidation number is zero
H oxidation number is usually +1 in acids
H2SO4 has H = +1, O = -2, then 2(+1) + S + 4(-2) = 0; S = +6
ZnSO4 S= +6, O = -2, then Zn + 6 + 4(-2) = 0; S = +2
H2 is an element, so its oxidation number is zero
Then we have S and O unchanged and the redox half reactions are
Zn  Zn +2 + 2 e- is an oxidation, because the electrons are on the product side
Zn is being oxidized, then it is a reducing agent
2 H+ + 2 e-  H2 is a reduction, because the electrons are on the reactant side
H+ is reduced, so it is an oxidizing agent.
33. Balance the following redox equations
Fe2+ + Cl2  Fe3+ + ClMnO4- + H2O2  Mn2+ + O2
http://www.chemguide.co.uk/inorganic/redox/equations.html
2 Fe2+ + Cl2  2 Fe3+ + 2 Cl2 MnO4- + 5 H2O2 + 6 H+  2 Mn2+ + 5 O2 + 8 H2O
34. Compare and contrast alpha, beta and gamma radiation. Include particle makeup,
frequency and health side effects.
Alpha radiation is released from the nucleus of an atom as 2 protons and 2 neutrons.
The protons give the alpha particle a positive charge. They have a high amount of
kinetic energy but can be easily stopped by paper or fabric. They can damage living
tissue such as skin.
Beta radiation result when a neutron breaks apart into one proton and one electron.
They have an overall negative charge and move faster than alpha particles, so they are
more difficult to protect against. Beta particles are able to penetrate cloth and paper
and can deeply penetrate skin and harm or kill living tissue. Thin metal substances (such
as aluminum) are able to stop beta particles, which are then absorbed by the material.
Gamma radiation is given off as gamma rays they are a form of electromagnetic waves
with a very high frequency and higher amount of energy than UV or X-rays. They have
higher energy than both alpha and beta. They penetrate most materials and therefore
cause the most damage to living cells. They can be stopped by layers of lead (think of
the lead apron when you get an X-ray).
35. If the half-life of a given substance is 300 days, how long will it take for a 80 gram
sample of the substance to decay until there is only 5.0 grams of the radioactive
substance remaining?
80 grams 40 grams = 1 half-life
40 grams  20 grams = 1 half-life
20 grams  10 grams = 1 half-life
10 grams  5 grams = 1 half life.
300 days x 4 half lives = 1200 days.
36. Compare fission and fusion.
Nuclear fusion is where two atoms with lighter nuclei combine to create an atom with a
heavier nucleus. Nuclear fission is when an atom with a large nucleus is split apart
releasing energy and radioactive particles. Both reactions produce large amounts of
energy.
37. Name 3 different safety precautions that should be taken for nuclear reactions to
occur.
Water cooling tanks
Control Rods
Proper disposal of waste
Radiation badges for worker protection
38. Which of the following is not an example of renewable energy sources?
Solar
Wind
Water
Coal
39. Ozone depletion is caused by man-made chemicals, what are some side-effects of the
reduction in the Ozone layer?
Skin cancer
Cataracts
Impaired Immune Systems
Reduced crop yields of sensitive crops such as soybeans and corn.
40. What properties of Carbon make it able to be a part of such a variety of compounds?
It is able to form single, double and triple bonds and multiple shapes.
Carbon is the able to form different molecular shapes
41. Identify at least 2 ways that our society can use to conserve energy.
Examples include use of compact fluorescent light bulbs, carpooling, set thermostat
higher (78oF) and recycling. Other examples possible.
42. Identify 4 different types of biotechnology.
Types of biotechnology: genetic modification of crops, stem cell research, DNA forensic
science, creation of vaccines and medicine