Helen Ma
Flashcards by Helen Ma, updated more than 1 year ago
Helen Ma
Created by Helen Ma over 5 years ago


test review for equilibrium unit, grade 12 chemistry

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Question Answer
What is Le Chatelier's Principle? If an outside influence upsets an equilibrium, the system undergoes a change in direction that counteracts the disturbing influence and the system reaches a new state of equilibrium.
What are the 5 factors effecting equilibrium? 1. Concentration 2. Temperature 3. Pressure 4. Addition of Inert Gases 5. Presence of a Catalyst
How does changing the concentration of products or reactants effect the equilibrium? increase concentration of products --> shift towards reactants; increase of concentration of reactants --> shift towards products
How does changing pressure or volume effect equilibrium? Less volume --> greater pressure --> shift towards side with less amount of particles (side with less moles) to ease pressure; if amount of moles on each side of rxn are the same then equilibrium is unchanged; changing pressure will only effect gases
How does changing the temperature effect equilibrium? If the rxn is exothermic (releases energy), an increase in temp causes the rxn to shift to reactants; decrease in temp, shift products; If the rxn is endothermic (absorbs energy), an increase in temp causes the rxn to shift to products; decrease in temp, shift reactants
How does adding inert gases effect the equilibrium? It is negligible so it does not change the equilibrium
What is a reversible reaction? A rxn where both its forward and backward rxn occurs simultaneously in a closed system at all times.
What is a chemical equilibrium? When the rate of the forward and backward rxns are equal and no change can be observed. It does NOT mean that the concentrations of reactant and product are equal.
What are the 4 factors to reach equilibrium? 1. Closed system 2. simultaneous opposing rxns occurring at the same time 3. equilibrium was reached by starting with reactants or products 4. temp is kept constant (bc equilibrium rates change w/ temp change)
How can enthalpy and entropy to used to predict reaction occurrence? Enthalpy: will favour direction that releases energy; Entropy: will favour direction where it becomes more chaotic (changes state to a less organized state or towards the side with more moles) Enthalpy + Entropy favours forward --> rxn will be completed Enthalpy + Entropy favours backwards --> rxn will not be completed Enthalpy + Entropy favour different directions --> reaction reaches equilibrium
How does adding a catalyst change the equilibrium? It does not change the equilibrium because it effects both forward and backward activation energy; in other words, since it speeds up with directions of the rxn with the same extent, it does not actually change the position of the equilibrium
What is the equilibrium law and units for Keq? Keq = ([products]^a ) / ([reactants]^b) where a is the coefficient of the product and b is the coefficient of the reactant; it can always be developed from the BALANCED chemical eqxn; there are no units for Keq
What is Keq and how can you use the value of Keq to predict which way a reaction favours? Keq is the equilibrium constant that describes the ratio of the concentration of reactants to products Keq > 1 equilibrium is shifted towards product, closest towards completion; Keq < 1 equilibrium is shifted towards reactants, furthest from completion; Keq = 1 equilibrium is right in the middle, so concentration of products and reactants are the same
How can you manipulate Keq values to find the Keq of a related reaction? If you inverse the first rxn to get to the second --> 1/Keq If you multiply the first rxn by a to get the second --> (Keq)^a If you take the sum of two rxns, multiply their Keqs together to get the sum of the Keq
When writing equilibrium laws, what can you exclude? Solids and liquids
Will temperature change the value of Keq? Yes, because the rxn will shift to one side, changing the concentrations of product and reactant, and thus changing the Keq, which is based on these concentrations.
What is Ksp? It is the solubility product constant for solutions that can form a solid. It is the equilibrium constant between a compound and its composite ions. It describes the degree to which a compound disassociates in water.
What is the difference between Ksp and Keq? When writing the Ksp, you only need to include concentrations of usually one side (side with ions, ignoring the solid). When writing Keq, typically, concentrations of both sides are included (unless solid or liquid).
What is molar solubility? Molar solubility of a compound is the concentration that is necessary for a solution to become saturated (reach equilibrium.)
What is saturation? A saturated solution refers to one where no more solute can be added without forming a precipitate. At the saturation point is also the equilibrium point.
Which elements are always soluble? All group 1 metals (Li, Na, K, Rb, Cs and Fr) and nitrates.
What is the significance of the magnitude of Ksp? The higher the Ksp is, the more soluble the compound. The lower the Ksp, the less soluble the compound.
How can you predict whether or not a precipitate will form? You compare the experimental value (Q) using information given to the actual Ksp value. Q < Ksp no ppt. Q = Ksp no ppt. Q > Ksp ppt.
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