UTC: Thursday, February 21st, 2019

LO 6.25….AGAIN!

Having looked at the “thermal energy” nonsense in LO 6.25 for around 5 years, and having written this blog post in Feb 2016, and this blog post in Feb 2015 (you should read them both), I still feel lost when it comes how TE might ultimately be assessed. With only one MCQ ever written about […]

All creatures great and small and 2016, 6

All things bright & beautiful, all creatures great and small. Remember that hymn? We often talk about remembering the little things, well here’s a lesson in remembering the big things as well! This post started life with an entirely different title. It was initially called, Should I ignore ‘-x’ in my ICE table? I started writing […]

Another ∆G° mystery

We’ve lived through the nonsense of the inclusion of PES in the new AP Chemistry curriculum. Many think the exclusion of quantum numbers, stinks. Some people HATE the removal of colligative properties from the course. For me, these (and other things) provoke varying degrees of outrage that range from complete indifference to utter incredulity. Then […]

Writing good answers to AP Equilibrium problems

Here’s the latest in the ‘writing good answers’ series, Writing good answers to AP Equilibrium problems. This post only deals with aspects of equilibria such as Kc, Kp, Ksp and Le Châtelier’s Principle – I’ll deal with Acid-Base equilibria in a separate post. So, here’s a list of some pointers to make your AP equilibrium […]

Le Châtelier’s principle in action

Following the mention of the cobalt(II) complex ion system in this post from a couple of days ago, here’s a 30 second video clip of Le Châtelier’s principle in action in the same (with The Smiths). The equilibrium that is set up is this, [Co(H2O)6]2+(aq) + 4Cl–(aq) ⇌ [CoCl4]2-(aq) + 6H2O(l) and the aqueous solution […]

Water in equilibrium mixtures and Le Châtelier’s principle

When it comes to water in equilibrium mixtures and Le Châtelier’s principle, things can be confusing, so let’s try to take some of the mystery out of this. When reading EK6B1a in the AP Chemistry CED, one finds this; The final few words are what I care about here. Where water is important I think […]

∆G and ∆G° revisited

∆G and ∆G° can be tricky things. This is partly evidenced by a post that I wrote back in January of 2012 continuing to be one of the most popular of all time on the blog. I wrote that post four years ago in an attempt to clear my own mind about the differences between […]

‘Expanded LCP’ or ‘Q versus K’ explanations?

It’s never been OK, on the AP exam, to offer a simple, ‘because of Le Châtelier’s principle‘ argument as the explanation for the shift of an equilibrium position caused by an external stress. This is in much the same way that it has never been acceptable to say, ‘because as you go across the period first […]

Inert gases and gaseous equilibrium mixtures

What happens when an inert gas is added to a gaseous equilibrium mixture at constant volume? Before we answer that question, it might be worth defining what we mean by “an inert gas”. In this context we mean a gas that is not involved in the equilibrium reaction, or one that reacts with any of […]

Why does increasing T, speed the ENDO direction *more* than the EXO direction?

In an imminent update to the Unit 6 notes, I have included an ‘explanation’ of why reactions with larger activation energies (i.e., the endothermic process in any equilibrium system – see the diagram below), have their rates of reaction increased to a greater degree than reactions with smaller activation energies (i.e., the exothermic process in […]