Question

An unknown molecule contains only sulfur atoms. Suppose 1 L of vapor of this 20) molecule is reacted with sufMicient oxygen at 1 atm and 500 °C to produce 8 L of SO2 gas. How many sulfur atoms does the unknown molecule contain in the vapor phase?

A) 8 B) 3 C) 2 D) 4 E) 6

If one mole of water (~18 mL, the system) is vaporized from liquid to gas at 100o C, the amount of work done on the surroundings is 2.5 kJ, while the change in internal energy for the system is 38.2 kJ/mol. What is the amount of heat required to vaporize one mole of water?

A) 38.2 kJ B) 35.7 kJ C) O40.7 kJ D) 40.7 kJ E) O35.7 kJ

One mole of an ideal gas is expanded from a volume of 1.00 L to a volume of 10.00 L against a constant external pressure of 1.00 atm. How much work (in joules) is performed on the surroundings?

A) 456 J B) 912 J C) 0.013 J D) 2740 J E) 2870 J

PLEASE SHOW WORK

Answer 1

Question :- One mole of an ideal gas is expanded from a volume of 1.00 L to a volume of 10.00 L against a constant external pressure of 1.00 atm. How much work (in joules) is performed on the surroundings?

Answer :-

work = -P(delta V) = -(1.00 atm)(9.00 L)

1.00 atm x (101,300 Pa / atm) = 101,300 Pa = 101,300 N/m^2

9.00 L = 9.00 dm^3 x (1 m / 10 dm)^3 = 0.00900 m^3

work = -(101,300 N/m^2)(0.00900 m^3)

= 912 N m = (B) 912 J

Question :- If one mole of water (~18 mL, the system) is vaporized from liquid to gas at 100o C, the amount of work done on the surroundings is 2.5 kJ, while the change in internal energy for the system is 38.2 kJ/mol. What is the amount of heat required to vaporize one mole of water?

Answer :-

We know that delta (U) = W + q

where delta (U) = internal energy for the system is 38.2 kJ/mol.

                       W = amount of work done on the surroundings is 2.5 kJ

                       q = amount of heat required to vaporize one mole of water

so putting all value in above equation

q = delta (U) - W

q = (38.2 kJ/mol x 1 mol ) - 2.5 kJ

q = 35.7 kJ = B) 35.7 kJ