We’ve said it’s not just enthalpy that determines whether reactions can happen…
That something called entropy plays a role too.
So, okay…what is entropy?
Well, just like how all matter has a mass…and a temperature…and a volume…all matter has an entropy. It’s a property that matter has.
That means that chemists can say things like ‘gold has an entropy of 47.4 joules per kelvin per mole’ [S(Gold) = 47.4 J K -1 mol -1 ]
So, which of these sentences might make sense?
These sentences might make sense since they all treat entropy as a property of matter.
Okay, so entropy is a property of matter. What else?
Well, entropy is hard to describe using words.
That’s because, unlike mass, temperature and volume, it isn’t a property that we can directly feel, see, sense, or measure
Really, the best, most precise way to understand the abstract world of entropy is with maths – and we’ll actually explore that maths a little later.
But for now, we can consider entropy to be a measurement of disorder.
And we can say that, the higher the disorder of a something, the higher it’s entropy.
But while we’re comfortable comparing the disorder of everyday objects, how on earth do we compare the disorder of chemicals?
For example, how do we compare the disorder of a glass of water at 25 degrees and a glass of water at 26 degrees?
Well, to do that, we need to dive down into the atomic scale, which we’ll do shortly.
But before we do, let’s pad out this woefully empty factfile with a bit of historical context
Entropy was first introduced by Rudolf Clausius in 1865.
Clausius is commonly remembered as one of founding fathers of thermodynamics, but he’s also remembered for being the scientist with the most christmassy name.
And Clausius gave entropy the symbol, S – after the scientist Nicholas Sadi-Carnot, whose work laid the foundations for this area of research.
So, to sum up, entropy is…
Entropy is a measurement of disorder.
The more disordered something is, the higher its entropy. And lastly, to represent entropy, we use the capital letter S.
