Write Balanced Chemical Equations for the Following (including ALL physical states)

Question

10. When heated, solid lithium chlorate decomposes to produce solid lithium chloride and oxygen gas.

11. When solid silicon dioxide is added to hydrofluoric acid, gaseous silicon tetrafluoride and liquid water are produced.

Answer 1

Here are the basic tools you need to answer the question:

1. You need to understand the naming of compounds (nomenclature) for ionic and molecular compounds.
2. You need to understand the symbols used to write a chemical equation.
3. You need to understand the process used to balance chemical equations.

Step 1: What is the problem asking? It mentions balancing equations from words, so you need a periodic table and a list (perhaps memorized if required by your teacher) of polyatomic ions. This allows you to assemble your puzzle pieces of ions. Also, the problem mentions balancing the equation using symbols to indicate the states, so you need to be familiar with solid (s), liquid (l), gas (g) and aqueous (aq) notation. Once this is set up, then you can finally balance the equation using only the coefficients.

Step 2: Develop a plan.

A. We need to first translate the written names into elemental symbols.

B. Then, we can put those formulas into the form of an equation.

C. Finally, balance the equation to obey the law of conservation of mass.

Step 3: Execute!

A. Lithium chlorate is the first compound mentioned. As soon as I see that compound, I look if it is ionic or covalent. I see a metal (lithium), so I know that I will need to know the charge (+1, because it is in the first column of the alkali metals). Lithium is followed by the word chlorate; the -ate ending means that I have to refer to my list of polyatomic ions. The -ate ending means you have one more oxygen atom "ate more pizza" (oxygen reminds me of pizza). Knowing my list, chlorate is ClO₃^-. To combine Li⁺ and ClO₃^-, it is actually pretty easy, as it is a 1 to 1 ratio. It takes one Li⁺ to "cancel" one ClO₃^-, so the formula is LiCO₃. The next compound mentioned is lithium chloride. I see a metal (lithium), so I know that it is ionic. This again is the +1 lithium ion. This time, the second part is chloride. The -ide ending, in this case, tells me that it is simply chlorine from the periodic table. Chlorine is in halogen family, right next to the noble gases. What is the charge? -1 is the charge. So Li⁺ is bonded with Cl^-. The formula is LiCl. The last compound mentioned is oxygen. Remember, oxygen is one of the seven diatomic elements. It is found as O₂. Now we have all of our compounds.

B. We now can take those formulas and place them into and unbalanced form.

LiClO₃ is decomposing, so it is the only reactant we are also told that it is a solid and it is heated. There are a few ways to show it is heated (Δ is often placed above the yield arrow→ to show heat was added), so:

LiClO₃(s) -- ^Δ→

The LiCl is a solid, and the O₂ is a gas, giving us:

LiClO₃(s) --^Δ→ LiCl(s) + O₂(g)

C. OK, now the next part of the plan is to balance. Remember, you can only change coefficients, not subscripts. To keep track of this, make a table to keep track of numbers of atoms. This can be drawn different ways, but put the reactant numbers on the left and the product numbers on the right. List each element and the numbers of that atom on each side:

R __________P

1 Li 1

1 Cl 1

3 O 2

So, the number of oxygen atoms is not balanced. We can only change the coefficients, so how can I put the correct coefficient in front the compounds containing oxygen? One thing to notice here is that no matter what number that you put in front of the O₂ on the right, it will always be an even number. Since ClO₃ has O in multiples of 3, it will have to be made into an even number to balance. The "2-3" or "3-2" theme is one that comes up quite a bit, so it is helpful to remember that they are factors of 6.From that, we place a 2 in front of the LiClO₃, and a 3 in front of the O₂:

2 LiClO₃(s) --^Δ→ LiCl(s) + 3 O₂(g)

Keep in mind that the coefficients change the number of atoms in each element of the compound, so now we have:

R __________P

2 Li 1

2 Cl 1

6 O 6

How can this be fixed? If I put a 2 in front of the LiCl on the right, it solves the problem:

2 LiClO₃(s) --^Δ→ 2 LiCl(s) + 3 O₂(g)

R __________P

2 Li 2

2 Cl 2

6 O 6

Step 4: Check your answer. You've come too far to make a goof-up cost you, so check if you answered everything that the problem asked for:

1. Are the formulas right for the compounds?
2. Is the equation written in the proper form, including the required symbols?
3. Is the equation balanced?

For the next equation, repeat the same steps (I won't head into the detail that I just did). Try the second equation before you read on.

Step 1: The equation is asking for a balanced equation, requiring proper formulas for compounds, so a periodic table is needed and, possibly, a list of polyatomic ions. You need to use symbols for their states. We need to be able to balance this at the end.

Step 2: Make a plan. Just like before, make sure that you have the right formulas. Next, put those formulas into an equation. Balance the equation. Finally, check your work.

Step 3: Execute!

A. Silicon dioxide is the first compound mentioned. It has two nonmetals, so this is a molecular compound. There is no need to mess with charges. The prefixes tell me that the formula is SiO₂. Hydrofluoric acid involves naming rules that your teacher may or may not have told you (some teachers just may give you a list to know). Hydro means that it starts with H; the -ic coupled with the hydro means that this compound is HF. The next compound is silicon tetrafluoride. Again, two nonmetals tells that it is a molecular compound, and the prefixes tell you the number of atoms. From this you have SiF₄. Water is simply H₂O. Those are all of the compounds.

B. Let's put the formulas into the unbalanced equation. The SiO₂ is a solid. Hydrofluoric acid, like all acids in reactions like this, are aqueous (aq). The SiF₄ is listed as a gas. H₂O is a liquid, so now you have:

SiO₂(s) + HF (aq) → SiF₄ (g) + H₂O(l)

C. The next part of the plan is to balance. Remember, you can only change coefficients, not subscripts. To keep track of this, make a table to keep track of numbers of atoms. List each element and the numbers of that atom on each side, like before:

R __________P

1 Si 1

2 O 1

1 H 2

1 F 4

You can start at a couple of places here. In this example, it's fine to start with O (in different examples, I like to hold off on O if it is in more than one compound on the same side). Putting a coefficient of 2 on the right in front of the H₂O gives you:

SiO₂(s) + HF (aq) → SiF₄ (g) + 2 H₂O(l)

R __________P

1 Si 1

2 O 2

1 H 4

1 F 4

Notice that H and F are still not balanced, so what coefficient can you use? A 4 in front of HF gives you:

SiO₂(s) + 4 HF (aq) → SiF₄ (g) + 2 H₂O(l)

R __________P

1 Si 1

2 O 2

4 H 4

4 F 4

Step 4: Check your answer. You've come too far to make a goof-up cost you, so check if you answered everything that the problem asked for:

1. Are the formulas right for the compounds?
2. Is the equation written in the proper form, including the required symbols?
3. Is the equation balanced?

I hope this helped. Take care.