When water decomposes into oxygen and hydrogen, the mass
A. increases
B. varies according the number of hydrogen and oxygen molecules that form.
C. remains constant
D. decreases
mass does not change in a chemical reaction
In order to determine how the mass changes during the decomposition of water into oxygen and hydrogen, we need to understand the concept of conservation of mass. According to the law of conservation of mass, mass is neither created nor destroyed in a chemical reaction.
The balanced chemical equation for the decomposition of water is: 2H2O -> 2H2 + O2. From this equation, we can see that two molecules of water (H2O) decompose to form two molecules of hydrogen gas (H2) and one molecule of oxygen gas (O2).
Now, let's consider the mass of each component involved.
One molecule of water (H2O) has a molar mass of approximately 18 grams. So, two molecules of water will have a total mass of 36 grams (18 grams/molecule x 2 molecules).
Two molecules of hydrogen gas (H2) have a molar mass of approximately 4 grams per mole. Therefore, the total mass of the hydrogen gas produced is 8 grams (4 grams/molecule x 2 molecules).
One molecule of oxygen gas (O2) has a molar mass of approximately 32 grams. So, the total mass of the oxygen gas produced is 32 grams (32 grams/molecule x 1 molecule).
Now, let's sum up the masses of the products: 8 grams (hydrogen gas) + 32 grams (oxygen gas) = 40 grams.
Comparing the mass of the products (40 grams) with the initial mass of the water (36 grams), we can see that the mass increases during the decomposition of water into oxygen and hydrogen.
Therefore, the correct answer is A. The mass increases.