Connie and Dewayne know that solid potassium reacts very strongly with water, producing a chemical called potassium hydroxide along with hydrogen gas. They know the chemical equation looks like this.

2K + 2H 2 O → 2KOH + some amount of H 2

There are 4 atoms of hydrogen shown on the reactant side. How many total atoms of hydrogen must be on the product side?

1 answer

In the given chemical equation:

\[ 2K + 2H_2O → 2KOH + \text{some amount of } H_2 \]

Let's break down the number of hydrogen atoms.

On the reactant side, the water molecules (H₂O) contribute hydrogen atoms as follows:

  • Each water molecule (H₂O) has 2 hydrogen atoms.
  • Since there are 2 water molecules, the total number of hydrogen atoms from water is: \[ 2 \text{ (H₂O)} \times 2 \text{ (H per H₂O)} = 4 \text{ hydrogen atoms} \]

Now, looking at the product side, we need to account for:

  1. The potassium hydroxide (KOH):

    • Each KOH has 1 hydrogen atom.
    • Since there are 2 KOH produced, the total contribution from KOH is: \[ 2 \text{ (KOH)} \times 1 \text{ (H per KOH)} = 2 \text{ hydrogen atoms} \]
  2. The hydrogen gas (H₂):

    • Hydrogen gas (H₂) has 2 hydrogen atoms per molecule.
    • The amount of hydrogen gas produced must make up the remaining hydrogen atoms needed to balance the equation.

We can set up the equation to find how many H₂ molecules we need:

  • Total hydrogen on the product side must equal the total hydrogen on the reactant side.
  • We have the total on the reactant side as 4 hydrogen atoms and we accounted for 2 hydrogen atoms from the KOH: \[ 4 \text{ (reactants)} = 2 \text{ (from KOH)} + n \times 2 \text{ (from H₂)} \] where \( n \) is the number of H₂ molecules produced.

Solving for \( n \): \[ 4 = 2 + n \times 2 \] \[ 4 - 2 = n \times 2 \] \[ 2 = n \times 2 \] \[ n = 1 \]

This means there is 1 molecule of H₂ produced. Now we calculate the total hydrogen atoms on the product side:

  • From KOH: 2 hydrogen atoms
  • From H₂: \( 1 \times 2 = 2 \) hydrogen atoms

Total hydrogen on the product side: \[ 2 \text{ (from KOH)} + 2 \text{ (from H₂)} = 4 \text{ hydrogen atoms} \]

Thus, the total number of hydrogen atoms on both sides confirms that they balance at 4 hydrogen atoms.

Final answer: 4 total atoms of hydrogen must be on the product side.