Every acid base reaction has 4 actors.
Before (or above) the arrow
The acid: this is the molecule giving up H+
The base: this is the molecule that receives H+
After the arrow
The conjugate base is the species formed after the acid has donated its H+
The conjugate acid is the species formed after the base has gained the H+
So the acid donates a proton, becoming the conjugate base, and the base accepts a proton, becoming the conjugate acid.
If you look at the patterns of bonds formed and bonds broken, it’s straightforward: we’re breaking the H-A bond and forming the H–B bond.
How can you tell if an acid-base reaction is favored or not? Here’s one clue: the conjugate acid should be a weaker acid than the starting acid, and the conjugate base should be a weaker base than the starting base.
How do we know if an acid-base reaction is favored or not? We have a tool for determining that! More tomorrow.
Thanks for reading! James