Reactions and Equations part deux

There's just a little bit more that I need to cover on Reactions, Equations and Stoichiometry before we're done with Unit 2A.(If you ask me, all this semester-long unit stuff is a bit off. Having year-long chunks is bad enough. When will people learn that learning is a continuous process, not a fragmented one? Yeah, sure, you sometimes learn stuff in leaps and bounds, but not according to someone else's schedule.. okay, I'll shut up now.)

First up is a few standard equations for you to remember. Remember how I said that when mixing two ionic substances together, the cations bond with different anions? As in, if you have NaCl and KF as reactants, you'd get NaF and KCl as products? Well, we're going to expand on that a bit more.

Acid and Base make a Salt and Water

This is your standard neutralisation reaction. When you have an acid, for example HCl, mixing with a base such as KOH, the K+ ion bonds with the Cl- ion to form the salt KCl. Now you have the H+ and OH- ions left. Two hydrogens and an oxygen make water.

HCl + KOH -> KCl + H₂O

Acid and Carbonate make a Salt, Carbon Dioxide and Water

This is slightly more complex, but not really. When you have an acid, such as HCl (it's just about the easiest acid to type on Blogger...) and a carbonate, such as Na₂CO_{3 (which is not so easy to type on Blogger and requires some copy-pasting from Word), what you first get is that the ions swap around, just like the other reactions we've covered so far. The Na+ and Cl- ions would bond to make the salt, NaCl. The carbonate and hydrogen ions would originally bond together to make carbonic acid,} H₂CO_{3, but because carbonic acid is unstable, it decomposes to form carbon dioxide and water. (At least, that's my understanding of it- please correct me if I'm wrong.)}

_{2HCl +} Na₂CO_{3 -> 2NaCl +} H₂CO_{3 +} H₂O

Note that I added coefficients to balance the above equation.

Acid and Metal make a Salt and Hydrogen Gas

When you have a reactive metal and an acid, the metal would first give up electrons to the hydrogen ions in the acid, becoming a positive ion. Then these positive ions would bond with the negative ions in the acid, forming a salt. (As for which metals are reactive- I'll talk about that when I talk about oxidation and reduction.) At the same time, the H+ ions receive the electrons from the metal, becoming H_{2 molecules, i.e. hydrogen gas. It probably all sounds a bit complex for now, but I promise it'll make sense when you learn about oxidation and reduction.}

_{Fe + 2HCl ->} FeCl_{2 +} H₂

The next important thing to talk about regarding chemical reactions is the writing of ionic equations. So far, we've been doing molecular equations. To convert molecular equations into ionic equations, just follow a few simple steps.

1. When you write out the molecular equations, make sure to write the state symbols as a subscript next to each substance. (I haven't been doing that so far, but hey, it's a pain writing subscripts on Blogger.) l for liquid, g for gas, s for solid and aq for ions in aqueous solution (i.e. dissolved in water).
2. Rewrite all of the aqueous substances out as individual ions. For example, write aqueous NaCl as Na+ and Cl-. Do this on both sides of the equation, but ONLY for aqueous substances (NOT liquids, solids or gases).
3. If an ion appears on both sides of the equation, cross it out on both sides.
4. The remaining substances make up your ionic equation. Yayyyyyyyyy.

Now I need to cover the last little bit of Stoichiometry of Unit 2A but I really can't be bothered doing that today, especially because it's stuff that I'll have to find examples for to explain it well (actually, a few of my other blog posts are in dire need of examples too). Maybe I'll get around to writing about Stoichiometry tomorrow. Maybe.