How many molecules are there in a 42.3 g sample of water, H2O?

In order to figure out how many molecules of water are present in that  

48.90-g

sample, you first need to determine how many moles of water you have there.

As you know, a mole is simply a very large collection of molecules. In order to have one mole of something, you need to have exactly  

6.022

⋅

10

23

molecules of that something - this is known as Avogadro's number.

In order to get to moles, you must use water's molar mass. A substance's molar mass tells you the mass of one mole of molecules of said substance.

Water has a molar mass of  

18.015 g/mol

. This means that one mole of water molecules has a mass of  

18.015 g

.

So, to sum this up,  

6.022

⋅

10

23

molecules of water will amount to  

1 mole

of water, which in turn will have a mass of  

18.015 g

.

Explanation:

answer is: c. the experiment shows that the red substance experienced a chemical change.

this is chemical change (chemical reaction), because two new substances are formed (metalig liquid and gas), the atoms are rearranged and the reaction is followed by an energy change.

this is example of chemical decomposition.

chemical decomposition (analysis) is the separation of a single chemical compound into its two or more elemental parts or to simpler compounds.  

chemical decomposition is opposite of chemical synthesis.

dynamic equilibrium is the answer.