Saved Bookmarks
| 1. |
One gram of water on evaporation at atmospheric pressure forms 1671cm3 of steam.heat of vaporisation at this pressure is 540 cal/gm. the increase in internal energy is....? a.250cal b.500cal 3.1000cal 4.1500cal |
|
Answer» = 1 gmpressure P = 1 atmvolume V = 1,671 cm³Let the ABSOLUTE temperature of water be = T ⁰K USING the ideal gas law: P V = n R T 1.013 * 10^5 * 1,671 * 10⁻⁶ = 1/18 mole * 8.314 J/⁰K/mole * T T = 366.48⁰Kwork done in expansion of the vapour from 1 cm³ water to 1671 cm³ vapour: at 1 atm. pressure: P (V2 - V1) = 1.013 * 10⁵ N/m² * (1671-1) * 10⁻⁶ m³ = 169.17 Joules = 169.17/4.184 cal = 40.43 CalLatent HEAT of vapourization = 540 cal / gm = 2257 J/gmThe increase in the internal ENERGY = latent heat - work done in expansion = 540 cal - 40.43 cal = 500 cal nearly. |
|