### Video Transcript

An acid–base reaction is described by the following equation: H2SO4 plus two NaOH yields Na2SO4 plus 𝑥 H2O. Find the value of the coefficient 𝑥.

In order to first solve this problem, let us remember the law of conservation of mass. It states that atoms can neither be created nor destroyed. Therefore, the number of atoms on the reactant side will equal the number of atoms on the product side. Remember that the reactants are on the left-hand side of the arrow and the products are on the right-hand side of the arrow. When balancing chemical reactions, it is useful to place all the atoms in the reactants and products below the chemical equation to ensure all atoms are balanced.

Let us begin this problem by first balancing the number of hydrogen atoms in the equation. On the reactant side, there are two hydrogen atoms in H2SO4 and two hydrogen atoms in two NaOH. Therefore, there are a total of four hydrogen atoms on the reactants side of the equation. Now, we will look at the product side; there are two hydrogen atoms in H2O. Since we need more hydrogen atoms on the product side, we need to add a coefficient to the water molecule. If we recall, a coefficient is a number placed in front of a chemical symbol or formula to show the number of molecules present in the balanced equation. Think of the coefficient as a multiplier. Since we already have two hydrogen atoms on the product side but need four, what would the multiplier of two be in order to have four atoms of hydrogen? It will be two since two times two is four.

Now that the hydrogen is balanced, let us make sure that the other atoms are balanced. Let us move on to sulfur. On the reactant side, there is one sulfur atom in H2SO4 and on the product side there is one sulfur atom in Na2SO4. Since sulfur is balanced, let us move on to balancing the oxygen atoms. On the reactant side, there are four oxygen atoms in H2SO4 and two oxygen atoms in two NaOH. So, there are six oxygen atoms in total on the reactant side. On the product side, there are four oxygen atoms in Na2SO4 and two oxygen atoms in two H2O. So, the oxygen atoms are balanced.

Finally, we need to ensure the sodium ions are balanced. There are two sodium ions in two NaOH on the reactant side and two sodium ions on the product side in Na2SO4. Therefore, the equation is balanced. So, the coefficient in 𝑥 H2O is two. Therefore, 𝑥 equals two.