CHEMICAL REACTIONS

ChemQuest 28

LiBr + P Li3P + Br2

Why is bromine written as Br2 on the right side?

Bromine is a diatomic molecule and always needs to be bonded to something; even bonding to itself works.

LiBr + P Li3P + Br2

Why is it not necessary for LiBr to be written as LiBr2?

If it were written LiBr2 it would not be a neutral compound.

Example Equation: Ca + HNO3 Ca(NO3)2 + H2

What are the reactants in the example equation in the above information section?

Reactants are written on the left side of the equation and so the reactants are Ca and HNO3.

Na + MgCl2 NaCl + Mg

Why can’t NaMg be produced?

Na+ cannot bond with Mg2+ because they are both positive.

Na + MgCl2 NaCl + Mg

Why can’t NaCl2 be produced?

Na+ only requires one Cl-. NaCl2 is not a neutral compound.

Na + MgCl2 NaCl + Mg

Are NaCl and Mg the only products that can be produced?

Yes.

Li + Ca3(PO4)2 Li3PO4 + Ca

Why can’t CaLi2 be produced?

Ca2+ and Li+ won’t bond because they are both positive.

Li + Ca3(PO4)2 Li3PO4 + Ca

Why can’t Li3P be produced?

Although Li3P is neutral, there is no P3- in the equation. There is only PO4

3- and we will almost never be breaking up polyatomic ions like PO4

3-.

Don’t mess with polyatomic ions!

Li + Ca3(PO4)2 Li3PO4 + Ca

Are Li3PO4 and Ca the only substances that can be produced?

Yes.

Write chemical equations for the following reactions.

Aluminum sulfate reacts with barium to produce barium sulfate and aluminum.

Al2(SO4)3 + Ba BaSO4 + Al

Magnesium reacts with copper(I) nitrate to produce magnesium nitrate and copper.

Mg + CuNO3 Mg(NO3)2 + Cu

Sodium reacts with calcium phosphide to produce sodium phosphide and calcium.

Na + Ca3P2 Na3P + Ca

Phosphorus reacts with sodium chloride to produce sodium phosphide and chlorine.

P + NaCl Na3P + Cl2 (Note that chlorine is diatomic!)

Each of the reactions you wrote in question 5 follows a similar pattern. The same pattern is followed by the equations in questions 3 and 4. Describe this pattern.

A single atom reacts with a compound and replaces one of the atoms in that compound.

How are reactions 5c and 5d different?

Na forms a positive ion (Na+) and

replaces another positive ion, but P forms a negative ion (P3-) and replaces another negative ion.

How are reactions 5c and 5d similar?

In both reactions a single atom replaces another atom from a compound that it is reacting with.

NaCl + Ag

AgCl + Na

(note: order is not important, so you could also write Na + AgCl)

Li + Ca3(PO4)2

Li3PO4 + Ca

(again, order is not important)