Test Example II
These are some examples from the last semester.  You should be able to feel what the test style is like for this class.

Part I, True/False questions
(One important key to improve your understanding is to find the answer why the statement is true or false.)
Formula mass and molar mass are the same thing!
A mole of any atom or molecule always contain the same number of that atom or molecule.
Oxidation reactions are always determined by gaining oxygen(s).
During chemical reactions, heat may be required or generated.
A chemical reaction is favored by decreasing in entropy.
Activation energy can prevent reactions to take place.
The activation energy for the forward reaction is always smaller than that of the reverse reaction.  This is why forward reactions are always more favorable.
    (How about endothermic reactions?)
Once an equilibrium is reached, it cannot be changed any more.
Once an equilibrium is reached, there is nothing going on.
Oxidation reactions are always determined by gaining oxygen(s).

Gas pressure is the result of simultaneous collision of gas particles on an object.
The air pressure on the earth is always 1 atm, i.e., 760 mmHg.
    (How about on the mountains? How about the pressure system of a hurrican, and the pressure system from the north in the winter?)
Particles have no kinetic energy at all at absolute zero.
Assuming constant pressure, if the temperature is doubled from 20 ºC to 40 ºC, the volume would be doubled.
Under the same conditions, 1 L of oxygen gas contains the same number of molecules as 1 L hydrogen gas even though their molecular mass are quite different.
Gas molecules travel at a very high speed even at room temperature.
All gaseous forms of molecules can be considered ideal gas.
The total pressure of a gas cylinder with 2 atm O2 and 3 atm N2 should be smaller than 5 atm because it is a mixture.

Multiple choice questions
(One important key to get multiple choice questions right is to find out reasons for each choice why or why not it is the correct one.)
Oxidation or reduction reactions of an element or a compound are characterized by all the followings except
             (1) oxygen may be involved.
             (2) electron may be involved.
             (3) change of the physical and chemical properties of the element.
             (4) the reactions must be very vigorous.
             (5) All the above are correct!

A false statement about entropy:
             (1) It is a measure of the disorder of a system.
             (2) Increasing entropy is a favorable pathway for a chemical reaction.
             (3) Liquid has higher entropy than solid.
             (4) A substance can have different entropy values.
             (5) Entropy is the only factor that determines whether or not a chemical reaction can occur.
(How about similar questions for heat and activation energy?)

Based on the following equation
              C3H8 + 5O2 ------> 3CO2 + 4H2O + heat
             you learn the following except
             (1) 1 molecule C3H8 react with oxygen to give 4 molecules of H2O.
             (2) the reaction can reach completion (i.e., burn out C3H8) with >5 mol O2.
             (3) C3H8 is burned spontaneously at room temperature.
             (4) heat is given off in this reaction.
             (5) 44 g C3H8 reacts with 160 g O2.

(What is the equilibrium constant Keq for the question above?)
(Do you know how to balance the above equation?  Now, try to write and balance the burning of pentane C5H10, or any alkane with the formula CnH2n+2, or any alkene with the formula CnH2n.)

The activation energy of a reaction
             (1) is not affected by a catalyst.
             (2) is always higher in an endothermic reaction than in an exothermic reaction.
             (3) is usually the same for a forward and a reverse reaction.
             (4) is changed by changing the temperature.
             (5) All the above are not correct!

The value of the Keq of a reaction is 4 x 107.  At equilibrium,
    (Think about the following question before you work on it.  Is the constant very large?  How about 4 x 10–7?)
             (1) the reactants are favored.
             (2) the reactants and products are present in equal amount in terms of moles.
             (3) the rate of the forward reaction is much greater than the rate of the reverse reaction.
             (4) the products are favored.
             (5) Can be determined without knowing the concentration of reactants and products.

Which of the following changes will cause the equilibrium position to move to the left?
                  4NH3(g) + 3O2(g) <===> 2N2(g) + 6H2O(g) + heat  (g:  gaseous form)
             (1) adding more O2
             (2) condense H2O(g) into liquid
             (3) heating the reaction
             (4) adding a catalyst
             (5) removing N2
    (How about move to right?)

How many moles of oxygen molecules are in 8.0 g oxygen gas?
             (1) 0.25 (2) 0.5  (3) 1.0  (4) 4.0  (5) 128
    (There are many more similar questions like this one, other gases and other compounds.)

The chemical formula of aspirin is C9H8O4.  What is the mass of 0.40 mol aspirin?
             (1) 45 g (2) 11g  (3) 72 g (4) 160 g (5) cannot determine
    (What do you need first in order to solve the above question?)

Chemical equilibrium is reached when
             (1) the concentration of reactants equals the concentration of products.
             (2) the reaction stops.
             (3) the forward reaction and the reverse reaction occur at the same time.
             (4) you don’t see and cannot measure anything change.
             (5) None of the above is a correct statement.

In which of these systems is entropy decrease?
             (1) air escaping from a bike tire
             (2) dissolving sugar in water
             (3) cooling a block of iron
             (4) melting snow

One mole of Mg(OH)2
             (1) has a mass 41.3 g
             (2) contains 6.02 x 1023 hydrogen atoms
             (3) contains 2 x 6.02 x 1023 oxygen atoms
             (4) contains total of 3 x 6.02 x 1023 Mg, O, and H atoms.
             (5) contains different number of Mg atoms from that of 1 mol Mg metal.

A false statement about atmospheric pressure:
             (1) There is no empty space (i.e., vacuum) in a tube 500-mm long with one end sealed which is filled with Hg
                    and is put into a Hg pool with the open end in the pool.
             (2) One atmosphere is the pressure required to support 760 mm of Hg.
             (3) One atmosphere is the pressure to support any other liquid substance to 760 mm height.
             (4) Gas pressure is the result of the kinetic energy of gas particles.

A gas mixture that contains oxygen, nitrogen, and helium with partial pressures 230, 440, and 150 mm Hg, respectively, in a container with a fixed volume
             (1) the pressure in the container is 440 mm Hg.
             (2) The number of oxygen molecules is 230/150 times more than the number of helium atoms.
             (3) there are equal numbers of the three gas particles in the container with a fixed volume.
             (4) when you decrease the volume by half, the partial pressures of all the three gases become twice higher.

What are the relationships between pressure (P) and volume (V) at constant temperature (T), P and T at constant V, and T and V at constant P?  Use words and equations to describe these relationships.

The pressure on 3.60 L of an anesthetic gas is changed from 780 to 376 mm Hg.  What is the new volume if the temperature remains constant?
             (1) 1.74 L      (2) 3.60 L     (3) 7.47 L     (4) cannot determine

An inflated balloon at 20.0 °C has a volume 2.0 L.  What is the volume when it is heated to 40.0 °C?
             (1) 4.0 L      (2) 1.0 L     (3) 2.1 L     (4) 1.9 L

Fill in the blanks/Questions and short answers

What is the equilibrium constant (Keq) for the reaction wA + xB <=====> yC + zD?
    (When Keq is very small, does the equilibrium favors the reactants on the left hand side or the products on the right hand side? Why?)

What is the equilibrium constant for the following equilibrium?
        HA + <=====> A–  + H+

The eqilibrium for CO2 to dissolve in water is shown below.
        CO2 + H2O <=====> H2CO3
Describe why should CO2 comes out out the liquid in a soda can when you open the can.  What is the principal that can describe this?  (Something about how to releave the "physical stress" added to a system.)

Complete (and balance) the following redox reaction.
         C2H5OH (ethanol) + sufficient amount of O2 ------>
    (Which one is reduced?)
    (Don't forget to review the seveal reactions we discussed in the class which are on the lecture note!)

Complete the equation for the redox reaction Mg + H2O ----->.
    Which one loses electron(s)?  Which one accepts electron(s)?

(Working with problems above gases below, what are the important things you need to keep in mind? Which physical property is proportional or inversely proportional to the other? What are the mathematical expressions for the proportionality and inverse proportionality?)

What is the volume of 16.0 g oxygen gas at 25 °C and a pressure of 0.5 atm?  (The gas constant is 0.082 atm L/mol K.)

What is the new volume of 1 L oxygen at 100 °C that is heated to 200 °C?

A gas with a volume of X L at 25 °C is heated until its volume is double.  What is the new temperature of the gas if the pressure is unchanged?

A balloon is filled with He to a volume of 50 L at 1.00 atm and 25 °C.  When it is released and rises to an altitude where the pressure is 380 mmHg and the temperature is –25°C.  What is the volume of the balloon at this new altitude?
An oxygen cylinder of 50 L at 25 °C has a pressure of 20 atm.  How long it will last for a patient if the flow rate is adjusted to 10 L/min? (Remember that once the oxygen is release from the gas cylinder, its pressure becomes 1 atm.)