Types of chemical reactions

Example 1: predict a single replacement

Problem Zinc metal is placed in copper(II) sulfate solution. Predict the products and write the balanced equation.

1. An element (Zn) plus a compound ($\mathrm{CuSO_4}$) means single replacement.
2. Check the activity series: Zn is above Cu, so zinc can replace copper.
3. Zinc forms $\mathrm{Zn^{2+}}$, so it pairs with sulfate as $\mathrm{ZnSO_4}$. Copper comes out as the metal.
   $$\mathrm{Zn + CuSO_4 \rightarrow ZnSO_4 + Cu}$$
4. Count atoms: Zn 1 = 1, Cu 1 = 1, S 1 = 1, O 4 = 4. Already balanced.

Answer $\mathrm{Zn + CuSO_4 \rightarrow ZnSO_4 + Cu}$, single replacement, coefficients 1, 1, 1, 1

Example 2: predict a double replacement

Problem Solutions of lead(II) nitrate and potassium iodide are mixed. Predict the products.

1. Two ionic compounds means double replacement. The ions are $\mathrm{Pb^{2+}}$, $\mathrm{NO_3^-}$, $\mathrm{K^+}$ and $\mathrm{I^-}$.
2. Swap partners: $\mathrm{Pb^{2+}}$ with $\mathrm{I^-}$ gives $\mathrm{PbI_2}$. $\mathrm{K^+}$ with $\mathrm{NO_3^-}$ gives $\mathrm{KNO_3}$.
3. $\mathrm{PbI_2}$ does not dissolve, so it forms a bright yellow solid. That precipitate is why the reaction happens.
4. Balance.
   $$\mathrm{Pb(NO_3)_2 + 2\,KI \rightarrow PbI_2 + 2\,KNO_3}$$

Answer $\mathrm{Pb(NO_3)_2 + 2\,KI \rightarrow PbI_2 + 2\,KNO_3}$, double replacement, coefficients 1, 2, 1, 2

Example 3: complete a combustion

Problem Write and balance the complete combustion of butane, $\mathrm{C_4H_{10}}$.

1. Complete combustion of a hydrocarbon gives $\mathrm{CO_2}$ and $\mathrm{H_2O}$.
   $$\mathrm{C_4H_{10} + O_2 \rightarrow CO_2 + H_2O}$$
2. Carbon: 4 $\mathrm{CO_2}$. Hydrogen: 5 $\mathrm{H_2O}$. Oxygen on the right: $8 + 5 = 13$, so $\tfrac{13}{2}\,\mathrm{O_2}$.
3. Double everything to clear the fraction.
   $$\mathrm{2\,C_4H_{10} + 13\,O_2 \rightarrow 8\,CO_2 + 10\,H_2O}$$

Answer $\mathrm{2\,C_4H_{10} + 13\,O_2 \rightarrow 8\,CO_2 + 10\,H_2O}$, coefficients 2, 13, 8, 10