4 g of hydrogen reacts with 20 g of oxygen to form water. The mass of water formed is

Options

A. 24 g
B. 36 g
C. 22.5 g
D. 40 g

Answer

To solve the problem of how much mass of water is formed when 4 g of hydrogen reacts with 20 g of oxygen, we can follow these steps:

### Step 1: Write the balanced chemical equation
The reaction between hydrogen and oxygen to form water can be represented by the balanced equation:
\[ 2H_2 + O_2 \rightarrow 2H_2O \]

### Step 2: Calculate the number of moles of hydrogen and oxygen
To find the number of moles, we use the formula:
\[ \text{Number of moles} = \frac{\text{mass}}{\text{molar mass}} \]

- For hydrogen (\(H_2\)):
- Mass = 4 g
- Molar mass of \(H_2\) = 2 g/mol
\[ \text{Moles of } H_2 = \frac{4 \, \text{g}}{2 \, \text{g/mol}} = 2 \, \text{moles} \]

- For oxygen (\(O_2\)):
- Mass = 20 g
- Molar mass of \(O_2\) = 32 g/mol
\[ \text{Moles of } O_2 = \frac{20 \, \text{g}}{32 \, \text{g/mol}} = 0.625 \, \text{moles} \]

### Step 3: Determine the limiting reagent
From the balanced equation, we see that:
- 2 moles of \(H_2\) react with 1 mole of \(O_2\).

Now, we need to find out how much \(O_2\) is required for the available \(H_2\):
- For 2 moles of \(H_2\), we need 1 mole of \(O_2\).
- Therefore, for 2 moles of \(H_2\), we require \(0.625\) moles of \(O_2\).

Now, we compare the available moles:
- We have 2 moles of \(H_2\) and 0.625 moles of \(O_2\).

Since \(O_2\) is less than what is required, it is the limiting reagent.

### Step 4: Calculate the moles of water produced
According to the balanced equation:
- 1 mole of \(O_2\) produces 2 moles of \(H_2O\).

Thus, \(0.625\) moles of \(O_2\) will produce:
\[ 0.625 \, \text{moles of } O_2 \times 2 = 1.25 \, \text{moles of } H_2O \]

### Step 5: Calculate the mass of water produced
To find the mass of water produced, we use the formula:
\[ \text{Mass} = \text{Number of moles} \times \text{Molar mass} \]

The molar mass of water (\(H_2O\)) is:
- \(2 \times 1 + 16 = 18 \, \text{g/mol}\)

Thus, the mass of water produced is:
\[ \text{Mass of } H_2O = 1.25 \, \text{moles} \times 18 \, \text{g/mol} = 22.5 \, \text{g} \]

### Final Answer
The mass of water formed is **22.5 g**.

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