If 30 ml of `H_2` and 20 ml of `O_2` react to form water, what is left at the end of the reaction ?

Options

A. 10 mL of `H_(2)`
B. 5 mL of `O_(2)`
C. 10 mL of `O_(2)`
D. 5 mL of `O_(2)`

Answer

To solve the problem of what is left after the reaction between hydrogen (H₂) and oxygen (O₂) to form water (H₂O), we can follow these steps:

### Step 1: Write the balanced chemical equation
The balanced equation for the formation of water from hydrogen and oxygen is:
\[ 2H_2 + O_2 \rightarrow 2H_2O \]

### Step 2: Determine the volume ratios
From the balanced equation, we can see that:
- 2 volumes of H₂ react with 1 volume of O₂ to produce 2 volumes of H₂O.
This means that 1 volume of H₂ reacts with 0.5 volumes of O₂.

### Step 3: Calculate the amount of O₂ needed for the given amount of H₂
We are given:
- 30 ml of H₂
To find out how much O₂ is required to react with 30 ml of H₂, we can use the ratio:
\[ \text{Volume of O₂ required} = \frac{30 \, \text{ml H₂}}{2} = 15 \, \text{ml O₂} \]

### Step 4: Compare the available O₂ with the required O₂
We are given:
- 20 ml of O₂ available
Since we need only 15 ml of O₂ to react with 30 ml of H₂, we can find out how much O₂ will be left after the reaction:
\[ \text{Remaining O₂} = \text{Available O₂} - \text{Required O₂} = 20 \, \text{ml} - 15 \, \text{ml} = 5 \, \text{ml} \]

### Step 5: Conclusion
After the reaction, there will be 5 ml of O₂ left unreacted.

### Final Answer
5 ml of O₂ will be left at the end of the reaction.

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