Question

Two identical flasks of the same volume are labeled A and B. Flask A contains NH₃(g) at   50_­­^oC and flask B contains HCl (g)_­ at 50^oC. KE=1/2 mv².

a) Which molecule is moving the most rapidly? Explain.

b) Give two ways you could increase the pressure in the flask containing the NH₃(g)

c) Do both molecules have the same kinetic energy? Justify your answer.

Answer 1

Both flasks are at same volume and same temperature.

Flask A contains NH3(molar mass =17g/mL) and falsk B contains HCl(molar mass 36.5g/mL).

QA) velocity of the two gases can be calculated by

RMS velocity = square root of 3RT/ M

Thus velocity is inversely proportional to molar mass, the gas with lower molar mass, that is NH3 moves rapidly at the same temperature.

QB) The pressure inside the flask containing ammonia can be incresed by

i) by increasing the temperature - as P and T are directly proportional provided V and numnber of moles are same, an increase in Temperature can increase the pressureinside the falsk.

ii) Alternatively , keeping the temperature same, we can decrease the volume of the container, ther by pressure ca be increased. Acording to Boyles' law presure and volume are inversely proportional. Thus a decrese in volume can increase the pressure.

QC)According to kinetic molecular theory, kinetic enrgy of the gas is proportional to its temperature. Thus the gases at same temperature have same kinetic energy.

The average kinetic energy of gas = 3/2 RT