To determine what is known about the reactants when the products of a reaction are [tex]\( \text{CO}_2 \)[/tex] and [tex]\( 2 \text{H}_2\text{O} \)[/tex], we can use the law of conservation of mass. According to this law, matter cannot be created or destroyed in a chemical reaction. This implies that the types and numbers of atoms present in the reactants must be the same as those present in the products.
Given:
Products:
- [tex]\( \text{CO}_2 \)[/tex] (carbon dioxide)
- [tex]\( 2 \text{H}_2\text{O} \)[/tex] (water)
Let's analyze the products:
1. [tex]\( \text{CO}_2 \)[/tex] contains:
- 1 carbon (C) atom
- 2 oxygen (O) atoms
2. [tex]\( 2 \text{H}_2\text{O} \)[/tex] contains:
- 2 molecules of water, each with 2 hydrogen (H) atoms and 1 oxygen (O) atom, giving a total of:
- 2 × 2 = 4 hydrogen (H) atoms
- 2 × 1 = 2 oxygen (O) atoms
So, in total, the products contain:
- 1 carbon (C) atom
- 4 hydrogen (H) atoms
- 2 + 2 = 4 oxygen (O) atoms
Since the products contain only carbon, oxygen, and hydrogen atoms, the reactants must also contain only these elements to satisfy the law of conservation of mass.
Now let's review the provided options:
A. The reactants include [tex]\( \text{CO}_2 \)[/tex] and [tex]\( \text{H}_2\text{O} \)[/tex].
- This option states that the reactants include the same substances that are products, but this is generally unnecessary for other substances containing C, O, and H to participate and be converted into these products.
B. The reactants include substances with only [tex]\( \text{C}, \text{O}, \text{H} \)[/tex] atoms.
- This option correctly states that the reactants include substances that only contain carbon, oxygen, and hydrogen atoms, which matches our analysis.
C. The reactants are also [tex]\( \text{CO}_2 \)[/tex] and [tex]\( \text{H}_2\text{O} \)[/tex].
- This is similar to option A in suggesting that the reactants are exactly the same products, which does not necessarily have to be true.
D. The reactants do not include any [tex]\( \text{C}, \text{O}, \text{H} \)[/tex] atoms.
- This statement contradicts our analysis, as it states that the reactants do not contain any of the atoms present in the products, which would violate the law of conservation of mass.
Therefore, the correct choice is:
B. The reactants include substances with only [tex]\( \text{C}, \text{O}, \text{H} \)[/tex] atoms.
