Question

In a chemical reaction, the elements magnesium and chlorine combined to form magnesium chloride (MgCl2). Which statement correctly describes the number of atoms in this reaction?
A.
There are just as many magnesium atoms after the reaction as there were before it.
B.
The number of magnesium atoms decreased in the chemical reaction.
C.
The number of chlorine atoms doubled in the chemical reaction.
D.
There are only a third as many atoms after the reaction as there were before it.

Answer 1

To analyze the statement regarding the reaction between magnesium and chlorine to form magnesium chloride (MgCl2), we can look at the basic principles of stoichiometry and the conservation of mass.

1. **Before the reaction**: Let's assume we start with 1 magnesium atom (Mg) and 2 chlorine atoms (Cl) since MgCl2 consists of 1 magnesium and 2 chlorine atoms.

2. **After the reaction**: We will have 1 magnesium atom and 2 chlorine atoms in the form of magnesium chloride (MgCl2).

Now, let's evaluate the statements:

A. **There are just as many magnesium atoms after the reaction as there were before it.**
- This statement is **true** because there is 1 magnesium atom before and after the reaction.

B. **The number of magnesium atoms decreased in the chemical reaction.**
- This statement is **false** because the number of magnesium atoms remains the same.

C. **The number of chlorine atoms doubled in the chemical reaction.**
- This statement is **false** because we start with 2 chlorine atoms and end up with 2 chlorine atoms in MgCl2, so it did not double.

D. **There are only a third as many atoms after the reaction as there were before it.**
- This statement is **false**. We started with 3 atoms (1 Mg + 2 Cl) and ended with 3 atoms (1 Mg + 2 Cl), so this comparison does not hold.

The correct answer is: **A. There are just as many magnesium atoms after the reaction as there were before it.**