pleaae answer both, i posted both questions separately last time, and i was give

Question

pleaae answer both, i posted both questions separately last time, and i was given the wrong answers for both of them.

in fact, lately Cheggs have been giving me the wrong answers for many questions I've posted.

thanks.

1. A 50.0 mL sample of a gas was found to have a pressure of 1.0 atm at 25 oC. What will be the new volume if the pressure is changed to 0.50 atm at constant temperature? 2. The temperature of 20.0 mL of certain gas was changed from 25.0°C to 50 °C at constant pressure. What is the new volume of the gas in mL?

Explanation / Answer

Ans. #1. Change in volume at constant temperature is given by Boyle’s Law: For a gas at constant temperature confined in a closed vessel, the product of pressure and volume is a constant.

            That is, PV = Constant                     - Temperature kept constant

Applying Boyle’s law for the given case-

            P1V1 (at 1.0 atm) = P2V2 (at 0.50 atm)

Putting the values in above equation-

atm x 50.0 mL = 0.50 atm x V2

or, V2 = (1.0 atm x 50.0 L) / 0.50 atm = 100.0 mL

Therefore, new volume = 100.0 mL

#2. Change in volume upon changing temperature on constant pressure is given by Charles’ law-

                        (V1/ T1) at 25.00 C = (V2/ T2) at 500C                    - P is held constant

Putting the values in above equation-

mL / 250C = V2 / 500C

or, V2 = (20.0 mL / 250C) x 500C = 40.0 mL

Therefore, new volume = 40.0 mL

Note: Ideal gas equation can be used to calculate the number of moles of gas in first conditions. Then new volume can be calculated using the variables in case 2. However, it does not affect the result caudated using Boyle’s or Charles Law as applicable.   

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