Balancing Equations (Chem.libretext example)

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The point of this exercise is to practice balancing reactions. Many students get overwhelmed when they face having to balance equation usually because it’s hard to determine where to start.

Given Problem: Lead (IV) Hydroxide and sulfuric acid react as:

Pb(OH)4+H2SO4→ Pb(SO4)2+H2O

Balance the equation:

1. The first step to balancing a chemical reaction is to identify how many molecules of each element are on either side of the arrow. Because of the law of conservation of mass, the number of moles of each element on either side must equal each other. That is why we know the given problem is unbalanced, because a number of moles on each side of the reaction are not equal.

I usually identify all of my different elements and write the number of them on each side of the equation. That way I can see which elements are unbalanced. This may not be the best way for you, some like to use metaphoric examples, others like to use models, etc. What’s important is that you correctly identify if there are any unbalanced elements, and by what ratio.

For example, Pb(OH)4 has 1 Pb molecule, 4 H molecules, and 4 O molecules. Not 1 Pb and 4 OH’s. An (SO4)2 molecule is not 2 SO4 molecules, but 2 sulfur molecules and 8 oxygens. Breaking compounds down like this will make balancing easier.

2. This is the full layout of elements in the reaction. We see that the lead is the only one balanced on each side of the equation. This means we must put the correct coefficients for each identity to balance the sulfur, oxygen, and hydrogen. It is a general rule of thumb to start with your larger or heavier objects first. In this case, I would balance the sulfurs and oxygens first, and end with hydrogen. If the leads were unbalanced, they’d be balanced first. It’s usually good rule of thumb to start your balancing with the biggest or heaviest species. Then, you can balance the smaller, more available species like O2(g), and H2(g) around the bigger molecules in the reaction.

3. This is the full balanced equation! As you can see, both sides of the equation are balanced. It may take some guess-and-checking to find the right coefficients, but it’ll get easier with practice.

This problem is courtesy of chem.libretexts.org, seeing as I forgot my work notebook for the break! Go ahead and check them out for further information, or for their method of balancing this equation.

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