Chem Equilibrium.pdf

Chemistry Study Guide 3 - Chapter 18By : TheStudentHelper

review for chapter 18 in regular chemistry

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Chemistry Study Guide 3 - Chapter 18

Chemistry Study Guide 3 - Chapter 18 1


Explain how the concentrations of A, B, C, and D change from the time when A and B are first combined tothe point of equilibrium. A + B -> C + D The concentrations of A, B, C, and D change because initially, the concentrations of C and D are zeroand A and B are at max. As A and B are used up, the concentrations change,

a) Write a general expression for an equilibrium constant.[C]x[D]y / [A]n[B]mb) What info is provided by K?The equilibrium constant for a specific temperature

In general, what reaction is favored if the value of K isa) Equal to one? -> neitherb) Very small? -> Reversec) Very large? -> forward

Forward or reverse reaction for the following pressure changes?a) Increased pressure -> Forwardb) Decreased pressure -> Reverse

In heterogeneous reactions, what types of substances do not appear in the equilibrium expression? Why? Pure liquids and solids because in an equilibrium expression, they are not affected by changes inpressure and are always a value of one.

Explain the effect of a catalyst on an equilibrium system. Catalysts speed up the process but neither favors a forward or reverse change.

Predict the effect of each for the equation:H2(g) + Cl2(g) > 2HCl(g) + 184 kJa) Addition of Cl2 -> forwardb) Removal of HCL -> forwardc) Increased pressure -> forwardd) Decreased temperature ->forwarde) Removal of H2 -> reversef) Decreased pressure -> reverseg) Addition of a catalyst -> no effect h) Increased temperature -> reversei) Decreased system volume -> reverse

How would A-I affect [HCl] and K value?a) [HCl] = increase; K = sameb) [HCl] = decrease; K = samec) [HCl] = same; K= samed) [HCl] = increase; K= increasee) [HCl] = decrease; K= samef) [HCl] = same; K= sameg) [HCl] = same; K= sameh) [HCl] = decrease; K= decrease


Chemistry Study Guide 3 - Chapter 18 2

i) [HCl] = same; K= no effect

Changes in the concentrations of the reactants and products have no impact on the value of K. Why? Such changes have an equal effect on the numerator and denominator of the chemical equilibriumexpression. So, all concentrations give the same value for K.

What relative (high or low) pressure would result in the production of the maximum level of CO2 in thisequation? 2CO(g) + O2(g) > 2CO2(g) High because the higher the pressure, the more the molecules collide, producing the max of productsavailable.

A combustion reaction proceeding in air under standard pressure is transferred to an atmosphere of pureoxygen under the same pressure.a) What do you observe? -> It would proceed at a faster rate.b) How can you account for this? -> Because of the increase in [O2].

What two factors determine the extent to which reacting ions are removed from solution? The solubility of the compound formed and, if the compound is soluble, on the degree of ionization.

Identify three conditions under which ionic reactions can run to completion. Formation of a gas -> H2CO3(aq) -> H2O(l) + CO2(g) Formation of a precipitate Formation of a slightly ionized product

Determine the value of each equilibrium constant.a) [A]= 2, [B]= 3, [C]= 4 answer: .67b) [A]= 1.5, [B]2= 2, [C]= 1.8, [D]3= 1.2 answer: .52

The value of K for the rxn below is 40.0. What would be the value of that constant for the reversereaction under the same conditions? K = .25

If M = 0.015mol/L for H2 + I2 2HI and K = 54.34, what is the [HI]? Get [HI] by itself. So, multiply 0.015x0.015 for the reactants and then multiply that with K. Squareroot that and your answer is [HI] = 0.111mol/L

Le Chateliers Principle When a system at equilibrium is disturbed by application of a stress, it attains new equilibriumposition that minimizes the stress. A stress is typically a change in concentration, pressure or temperature.

NB: Exothermic reactions move forward Endothermic favor reverse Cooling shift to the right; heating shifts to left

Common Ion Effect*The adding of an ion common to 2 solutes produces a precipitate that reduces ionization.

Vocabulary


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Reversible Reaction is a chemical reaction in which the products can react to re-form the reactants

Chemical equilibrium is a reversible chemical equation when the rate of its forward reaction equals the rate ofits reverse reaction and the concentrations of its products and reactants remain unchanged.


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