1 A flexible vessel is filled to a certain pressure with 390

1) A flexible vessel is filled to a certain pressure with 39.00 L of gas. Under conditions of constant temperature and moles of gas, how does the pressure of the gas change when the volume of the gas is decreased by a factor of two?

A. The pressure increases by a factor of four

B. Pressure decreases by a factor of three

C. Pressure increases by a factor of two

D. Pressure decreases by factor of four

E. Pressure remains the same

2) At a given temperature, molecules of different gases:

A. Have the same diameter

B. Have the same density

C. Have identical masses

D. Have the same kinetic energy

E. Have the same average velocity

Solution

Answers:

1. Since all other parameters remain unchanged, and Temperature and moles of gas are constant,

P1 V1 = P2 V2

But as the new volume of the gas (denoted by V2) is decreased by a factor of 2,

ie V2= 39/2 = 19.5 L

Thus, the equation becomes:

P2 x 19.5 L = P1 x 39.00 L

Therefore,

P2 = P1 (39.00/19.5) ;

P2 = P1 x 2

i.e. The pressure increases by a factor of 2, the correct option is Option C.

2. All gases at a given temperature have the \'same average kinetic energy\'. Hence, the correct option is option D. (The correct option is not enlisted, the word \'average\' is important.)

Explanation:

Properties like diameter (depends upon the number of electrons in an atom/molecule, it can be roughly same but it cannot be SAME), density (mass dependent property), masses and velocity (mass dependent property) are not the same for any two different gas molecules as the masses are different for all gas molecules.

The average kinetic energy of the molecules is proportional to absolute temperature.
At any given temperature, the molecules of all gases have the same average kinetic energy.