Writing / Balancing Equations

There are some concepts of chemistry that you should keep in mind when writing and balancing chemical equations: 

• Law of Conservation: Mass is not created nor destroyed in a chemical reaction. This means that the mass of reactants and products must equal. 

  • The number of atoms of each element must be the same on both sides of the equation. 

• Coefficients vs. Subscripts: Coefficients are placed in front of chemical formulas to indicate how many moles of a substance are in a reaction. Subscripts are placed within chemical formulas to indicate the number of particles per substance. 

• Reaction Types: Recognizing the type of chemical reaction can guide the balancing process. 

• Diatomic Elements: Elements like hydrogen, nitrogen, oxygen, fluorine, chlorine, bromine, and iodine naturally exist as diatomic molecules in their elemental form. 

• Polyatomic Ions: When polyatomic ions remain unchanged on both sides of the equation, treat them as single units when balancing. 

• States of Matter: Adding notations of states of matter to reactants and products provides context. 

Balancing chemical equations could be time-consuming and would largely rely on trial-and-error to figure out. 

An effective order for balancing chemical equations: 

1. Start by balancing metals first, as they often appear in fewer compounds. 

2. Next, balance nonmetals, excluding hydrogen and oxygen. 

3. Balance polyatomic ions if they remain intact throughout the reaction. 

4. Finally, balance hydrogen and oxygen, as they frequently appear in multiple compounds. 

Examples of Writing Molecular Equations with Steps: 

• Prompt: Hydrogen gas combusts with oxygen gas to form water vapor. 

1. Outlining the equation, H₂ + O₂ → H₂O is what we started out with, but the amount of atoms don't match up. 

2. Regarding the Law of Conservation, we ended up with: 2H₂ + O₂ → 2H₂O

3. Add states of matter if needed: 2H₂ (g) + O₂ (g) → 2H₂O (g)

• Prompt: Sodium metal reacts with chlorine gas to produce solid sodium chloride. 

  1. Outline the equation: Na + Cl₂ → NaCl

  2. Balance the equation: 2Na + Cl₂ → 2NaCl

  3. Add states of matter notations: 2Na (s) + Cl₂ (g) → 2NaCl (s)