Test 2- Ch. 17 Equilibrium State and Constant – Flashcards
Unlock all answers in this set
Unlock answers| Equilibrium |
Reactant and product concentrations stop changing because the forward and reverse rates have become equal rate(fwd) = rate(rev) |
| Equilibrium Constant K |
| K = (kfwd/krev) = [NO2]^2eq/[N2O4]eq |
Law of Chemical Equilibrium/ Law of Mass Action |
At a given temperature, a chemical system reaches a state at which a particular ratio of reactant and product concentrations has a constant value. Also, for a particular system and temp, the same equilibrium state is attained regardless of how the reaction is run |
| Reaction Quotient (Q) |
The particular ratio of concentration terms that is written for a given reaction At equilibrium: Q = K |
| Form of Q for an Overall Reaction |
If an overall reaction is the sum of two or more reactions, the overall reaction quotient (K) is the product of the reaction quotients(K or Q) for the steps: Koverall = K1 * K2 * K3*... |
| Relation of Q/K fwd and Q/K rev |
| Qc(fwd) = 1/Qc(rev) |
| Q for a Reaction w/ Coefficients multiplied by a common factor |
| If all the coefficients of the balanced equation are multiplied by some factor, that factor becomes the exponent for relating the reaction quotients and the equilibrium constants |
| Reactions Involving Pure Liquids or Solids |
-concentration of a pure solid and pure liquid is constant -since the concern is only w/ concentrations that change as they approach equilibrium these solid and liquid concentrations are not included in the reaction quotient |
| Qp- reaction quotient |
| The equilibrium constant obtained when all components are present at their equilibrium partial pressures is designated Kp, the equilibrium constant based on pressures |
| Relation of Kp and Kc |
-the exponent of the RT term equals the change in the amount (mol) of gas (delta(n) gas) from the balance equation, -1 Kp = Kc(RT)^(delta(n)gas) |
| Simplifying Assumption for Finding and Unknown Quantity |
-if a reaction has a relatively small k and relatively large initial concentration, the concentration change 'x' can often be neglected - if the assumption results in a change that is less than 5% the original concentration, the error is not significant, and the assumption is justified |
| Le Chatelier's Principle Applied |
| When a disturbance occurs, we say that the equilibrium; position shifts, which means that concentrations(or pressures) change in a way that reduces the disturbance, and the system attains a new equilibrium position (Q = K again) |
| Effect of; Change in Concentration |
Whenever the concentration of a component changes, the equilibrium system reacts to consume some of the added substance or produce some of the removed substance -note: the value of Kc does not change at given temp |
| Effect of an Inert Gas on Equilibrium Pressures |
| No effect on equilibrium |
| Effect of Pressure on Equilibrium |
If pressure increases, reaction shifts to the side with fewer moles of gas - change in volume results in change in concentration but does not change Kc |
| Effect of; Temperature on Equilibrium Position |
-A temperature increase(adding heat) favors the endothermic direction while a temperature decrease (removing heat) favors the exothermic direction -Temp rise will increase K for a system with a positive deltaH of reaction -Temp rise will decrease K for a system with a negative deltaH of reaction |
| Van't Hoff Equation |
| ln(K2)-ln(K1) = -(deltaH of reaction/R)*((1/T2)-(1/T1)) |
| Effect of a Catalyst |
| No effect on equilibrium position, just increases rate |
