Answer:
337.5kPa ~ 338kPa
Explanation:
Using the ideal gas law PV=nRT we have the following definitions from the problem:
V(initial) = 20cm³
P(initial) = ?kPa
V(final) = 75cm³
P(final) = 90kPa
Since we know that the number of moles of the sample did not change, nor did the temperature, nor does the ideal gas constant (R) we can rewrite this equation to state:
P(initial)V(initial) = nRT =P(final)V(final) ~ P(initial)V(initial) = P(final)V(final)
Rearranging this equation as we are solving for the initial pressure we find that:
P(initial) = (P(final)V(final))/V(initial)
P(initial) = ((90kPa)(75cm³))/20cm³
P(initial) = 337.5kPa ~ 338kPA