Topic 7.1 a) - EQUILIBRIUM
http://www.youtube.com/watch?v=JsoawKguU6A
*Opening Reflection Question: How does it feel to walk up the down escalator or run on a treadmill?
What remains constant?________________________
 What opposing processes occur at the same rate? _______________________________
*In both of these case, a state of _____________ _______________ has been achieved – a situation where at
least one property remains ___________ while opposing processes occur at the __________ rate.
Dynamic Equilibrium in Chemical Systems
 Many chemical reactions proceed in ________directions. (i.e., do not go to completion).
 These types of reactions are symbolized using ___________ arrows. Double arrows (
) represent
________________ reactions
or physical changes.
*Examples:
i) carbonic acid (a weak acid):
;
ii) the Haber process (production of ammonia)
 In a chemical system that achieves equilibrium, both the _____________reaction (i.e. the left-to-right
reaction) and the ________________reaction (i.e. the right-to-left reaction) proceed ________________ (this is
what the term “dynamic” is meant to convey) and at the __________ rate.
*Four Conditions that Apply to all Equilibrium Systems:
*1. The exact moment of equilibrium happens when the rate of the forward reaction __________ the rate of the
reverse reaction. If this is not the case, the system has _______achieved a state of equilibrium.
2. When a chemical system is in equilibrium, ________________ properties (those we can see, e.g. colour)
remain _______________. Furthermore, the ______________, _____________, and ____ of the system at
equilibrium all remain ______________.
3. Equilibrium can only be achieved in a ____________ system at a constant pressure. A closed system is a one
that may exchange ____________ but not ____________ with its surroundings.
4. Equilibrium can be approached from __________ direction (i.e. from the forward direction or from the
reverse direction). *What does this mean? *Consider the following equilibrium: N2O4(g)
2NO2(g)
Summary of Figure:
Recall: N2O4(g)
2NO2(g)
a) Flask initially contains exclusively N2O4 – 0.750 mol of it. Since N2O4 is written on the left side of the
equilibrium equation, we say that equilibrium is approached from the left.
c) Flask initially contains exclusively NO2 – 1.50 mol of it….exactly twice as much as in a). Why is this
important? Since NO2 is written on the right side of the equilibrium equation, we say that equilibrium is
approached from the right.
b) The concentrations at equilibrium are the SAME regardless of whether equilibrium is approached from the
left or right.
*OTHER EXAMPLES OF EQUILIBRIUM SYSTEMS:
A. Physical Processes:
i) _____________ Equilibrium:
H2O(l)
H2O(g)
ii) _______________ Equilibrium:
I2(s)
I2(aq)
CO2(g)
CO2(aq)
CaSO4(s)
Ca2+(aq) + SO42-(aq)
B. Chemical Processes
iii) _________________Equilibrium: H2(g) + I2(g)
iv) _________________Equilibrium:
2H2O(l)
2HI(g)
N2O4(g)
;
2H2(g) + O2(g)
v) ________-_________ Equilibrium: HC2H3O2(aq) + H2O(l)
;
2NO2(g)
CaCO3(s)
C2H3O2-(aq) + H3O+(aq)
CaO(s) + CO2(g)