[CH 1020] - Midterm Exam Guide - Ultimate 20 pages long Study Guide!

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Clemson
CH 1020
MIDTERM EXAM
STUDY GUIDE
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CH 1020 Chapter 12 Key Terms
Spontaneous process: a process that proceeds without outside intervention
Second law of thermodynamics: the principle that the total entropy of the universe
increases in any spontaneous process
Entropy (S): a measure of how dispersed the energy in a system is at a specific
temperature
Accessible microstate: a unique arrangement of the positions and momenta of the
particles in a thermodynamic system
Third law of thermodynamics: the principle that the entropy of a perfect crystal is zero
at absolute zero
Standard molar entropy (: the absolute entropy of 1 mole of a substance in its
standard state
Reversible process: a process that happens so slowly that an incremental change can be
reversed by another tiny change, restoring the original state of the system with no net
flow of energy between the system and its surroundings
Free energy: a measure of the maximum amount of work a thermodynamic system can
perform
Gibbs free energy (G): the maximum amount of energy released by a process occurring
at constant temperature and pressure that is available to do useful work
Standard free energy of formation (
: the change in free energy associated with the
formation of 1 mole of a compound in its standard state from its elements in their
standard states
Glycolysis: a series of reactions that converts glucose into pyruvate; a major anaerobic
(no oxygen required) pathway for the metabolism of glucose in the cells of almost all
living organisms
Phosphorylation: a reaction resulting in the addition of a phosphate group to an organic
molecule
CH 1020 Chapter 12 Textbook Notes
12.1 Spontaneous Processes
Chemical reactions like the combustion of gas-lamp fuel are examples of
spontaneous reactions: once started they proceed without outside assistance as long as
there are sufficient quantities of reactants available. The reverse reactionin this case,
converting carbon dioxide and water into fuel and oxygenis nonspontaneous: it cannot
happen on its own.
The word spontaneous can be a bit misleading because many spontaneous
reactions don’t start all by themselves: they need a little energy boost. However, once
initiated, a spontaneous reaction continues on its own. It is the self-sustaining nature of
these reactions that earns them the label spontaneous.
In addition, spontaneous does not necessarily mean fast.
Spontaneous is also not a symptom for exothermic. Some exothermic reactions
are not spontaneous, and some endothermic chemical reactions are spontaneous,
depending on reaction conditions. Consider, for example, the reaction that occurs when
baking soda (sodium bicarbonate) is added to room-temperature vinegar (dilute acetic
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acid). The foaming reaction mixture tells us that a chemical change is taking place and a
decrease in the temperature of the reaction mixture tells us that the reaction is
endothermic (∆Hrxn >0). A similar drop in temperature occurs when solutions containing
bicarbonate and calcium ions are mixed together.
Why are these two endothermic reactions spontaneous? The answer to this
question lies in something they have in common: the particles that make up their products
are more spread out and/or have more freedom of motion than the particles in their
reactants. The particles that make up ice or any crystalline solid occupy fixed positions,
and their motion is limited to vibrating in place without going anywhere. The particles in
liquids are more mobile: they are able to flow past and tumble over each other, which
means they have some translational and rotational freedom of motion. Therefore, when
either solid or liquid reactants form one or more products that are gases, there is a
substantial increase in particulate freedom of motion and the gas-phase particles are much
more spread out.
12.2 Entropy
Whenever an isolated thermodynamic system undergoes a change in which the
particles in the system disperse into a larger volume and/or gain freedom of motion, the
process is always spontaneous. The system is said to experience an increase in entropy.
The second law of thermodynamics states that the entropy of an isolated thermodynamic
system always increases during a spontaneous process.
In many science courses entropy is defined as disorder or randomness. Disorder
as applied to entropy does not mean messy or untidy, as in articles of clothing scattered
around a student’s bedroom.
The real meaning of entropy is linked to how energy is distributed in a
thermodynamic system. In particular, entropy (S) is a measure of how dispersed the
energy of a system is.
Energy dispersion can happen even when all the components of a system, or the
system and its surroundings, are at the same temperature.
Though kinetic molecular theory is a powerful tool for predicting that gases mix
spontaneously, there is another way to account for the spontaneity of mixingone based
on a statistical view of energy dispersion and entropy. We start with 2 red marbles
representing atoms of the other. Initially they are separated into two compartments. Then
the partition separating them is removed and the marbles are able to occupy any of the
marble-holding sites in either compartment. There are six ways to arrange the 2 red and 2
blue marbles among the 4 sites. In only two of these are the same color marbles in the
same compartment. In the other four they are mixed. If there is an equal chance any
marble could be in any one of the positions, then it is twice as likely that they will be
mixed together rather than separate.
Now consider what happens when we double the number of marbles and marble-
holding sites. If we allow all 8 of the marbles to be randomly arranged among the 8 sites
available to them, there are again only two possible arrangements in which each
compartment contains marbles of only one color. There are several mixing options: either
1 or 2 or 3 of the red marbles could end up on the side that originally contained only blue
marbles, and vice versa. The exchange of 1 marble produces four options for how to
arrange the blue one and the remaining 3 red ones in the originally all-red compartment.
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