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If a gas occupies a volume of 400cm\(^3\) at a temperature of 400K and a...

Chemistry
WAEC 2025

If a gas occupies a volume of 400cm\(^3\) at a temperature of 400K and a pressure of 1 atm, at what temperature and pressure would its volume be 200cm\(^3\)?

  • A. 800 K and 1 atm
  • B. 800 k and 0.5 atm
  • C. 200 k and 1 atm
  • D. 200 k and 0.5 atm
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Correct Answer: Option C
Explanation

To determine the correct conditions, we use the Combined Gas Law, which relates the pressure, volume, and temperature of a fixed amount of gas: 

        \(\frac{P\(_1\)V\(_1\)}{T\(_1\)}\) = \(\frac{P\(_2\)V\(_2\)}{T\(_2\)}\)

Given:

V\(_1\) = 400 cm\(^3\) , T\(_1\) = 400 K , P\(_1\) = 1 atm

V\(_2\) = 200 cm\(^3\) , T\(_2\) = ? , P\(_2\) = ?

We need to find which pair of pressure and temperature satisfies the equality 

P\(_1\)V\(_1\)/T\(_1\) = P\(_2\)V\(_2\)/T\(_2\)

First, calculate the initial constant:    

\(\frac{1 atm . 400cm{^3}}{400K}\) = 1

Now, test Option C

P\(_2\) = 1 atm

V\(_2\) = 200cm\(^3\)

T\(_2\) = 200 K

\(\frac{1 atm . 200cm{^3}}{200K}\) = 1

Options A, B and D will not give you 1.


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