Author Question: A substance has a melting point of 20C and a heat of fusion of 3.5 104 J/kg. The boiling point is ... (Read 117 times)

clmills979 · **on:** Jul 29, 2018

A substance has a melting point of 20C and a heat of fusion of 3.5 104 J/kg. The boiling point is 150C and the heat of vaporization is 7.0 104 J/kg at a pressure of 1.0 atm.

The specific heats for the solid, liquid, and gaseous phases are 600 J/(kgK), 1000 J/(kgK), and 400 J/(kgK), respectively. The quantity of heat given up by 0.50 kg of the substance when it is cooled from 170C to 88C, at a pressure of 1.0 atmosphere, is closest to
A) 30 kJ. B) 70 kJ. C) 44 kJ. D) 21 kJ. E) 14 kJ.

Question 2

A metal having a work function of 2.8 eV is illuminated with monochromatic light whose photon energy is 3.9 eV.

What is the threshold frequency for photoelectron production? (h = 6.626 10-34 J s, 1 eV = 1.60 10-19 J)
A) 6.8 1014 Hz
B) 2.7 1014 Hz
C) 7.6 1014 Hz
D) 8.5 1014 Hz
E) 9.4 1014 Hz