Unit 13: Fundamental Equilibrium Concepts
Why a finished-looking reaction is actually still running both ways at once, and how a pushed system settles into a new balance without undoing the push.
6 topics · 23 questions
Each topic is a path, not a menu: work down it in order and every question builds on the one above. Click any of them to watch the answer draw itself.
13.1 Dynamic Equilibrium
- How it worksHow can forward and reverse reactions both keep happening at equilibrium while every concentration stops changing?
- Common mistakeWhy isn't equilibrium a state where the reaction has simply stopped?
- Going furtherWhat happens to the forward and reverse reaction rates the instant a reaction reaches equilibrium, compared to right before?
Your turn1 of 2
A reaction reaches equilibrium and its concentrations stop changing. Why isn't equilibrium a state where the reaction has simply stopped?13.2 The Equilibrium Constant K
- How it worksHow does writing products over reactants, each raised to its coefficient, build the equilibrium constant expression?
- Worked exampleFind the equilibrium constant expression for the reaction N2 plus 3 H2 in equilibrium with 2 NH3.
- Common mistakeWhy aren't pure solids and pure liquids included in an equilibrium constant expression?
- Going furtherWhat happens to the value of K when a reaction's equation is flipped and written in reverse?
Your turn1 of 2
For the reaction N2 + 3 H2 in equilibrium with 2 NH3, find K given equilibrium concentrations of [N2] = 1.42 M, [H2] = 1.33 M, and [NH3] = 1.87 M.13.2 The Reaction Quotient Q versus K
- How it worksHow does comparing the reaction quotient Q to the equilibrium constant K reveal whether a reaction needs to move forward or backward?
- Worked exampleFind whether a reaction will shift forward or backward given Q = 0.50 and K = 4.0.
- Common mistakeWhy isn't Q calculated any differently from K, aside from using concentrations that aren't yet at equilibrium?
Your turn1 of 2
For the reaction 2 SO2 + O2 in equilibrium with 2 SO3, find the reaction quotient Q given current (not necessarily equilibrium) concentrations [SO2] = 1.42 M, [O2] = 1.33 M, and [SO3] = 1.87 M.13.4 ICE Tables and Equilibrium Calculations
- How it worksHow does an ICE table track the stoichiometric changes in every species as a reaction moves toward equilibrium?
- Worked exampleFind the equilibrium concentrations for a reaction starting at 1.00 M A and 1.00 M B, given a small equilibrium constant, using an ICE table.
- Common mistakeWhy can't you assume the change in concentration, x, is small enough to ignore in every equilibrium problem?
- Going furtherWhat happens to an ICE table's algebra when the equilibrium constant is so large that the reaction essentially runs to completion?
Your turn1 of 2
A reaction A + B in equilibrium with C starts at 1.54 M A and 1.54 M B, with no C present, and has a small equilibrium constant K = 0.00653. Using the small-x approximation (x is much smaller than 1.54), find the equilibrium concentration of A remaining (equilibrium [A] is approximately 1.54 times (1 minus the square root of K)).13.3 Le Chatelier's Principle: Changes in Concentration
- How it worksHow does adding or removing a substance shift a reaction toward whichever side relieves that change?
- Worked exampleFind which direction the equilibrium N2 plus 3 H2 in equilibrium with 2 NH3 shifts when additional NH3 is added.
- Common mistakeWhy doesn't adding more reactant change the actual value of the equilibrium constant K?
- Common mistakeWhy doesn't Le Chatelier's principle mean the stress applied to a system gets completely undone?
Your turn1 of 2
The reaction N2 + 3 H2 is in equilibrium with 2 NH3. Which direction does the equilibrium shift when additional NH3 is added to the system?13.3 Le Chatelier's Principle: Volume, Pressure, and Temperature
- How it worksHow does raising the temperature act like adding more of either the reactants or the products, depending on whether the reaction is endothermic or exothermic?
- Worked exampleFind which direction the equilibrium 2 SO2 plus O2 in equilibrium with 2 SO3 shifts when the container's volume is decreased.
- Worked exampleFind which direction an endothermic reaction's equilibrium shifts once the temperature is increased.
- Common mistakeWhy is temperature the one stress that actually changes the value of K, unlike a change in concentration or volume?
- Ties togetherHow does treating heat as a reactant or product in an endothermic or exothermic reaction unify all of Le Chatelier's temperature predictions?
Your turn1 of 2
A gas-phase equilibrium has an equilibrium constant Kc = 6.99 and a change in moles of gas (products minus reactants), delta n = 1. Find Kp at 392 kelvin, using Kp = Kc times (0.08206 times T) raised to the power delta n.