Question

a) Determine the amount of heat (q) necessary to heat 36.0 grams of ice (H2O (s)) from the solid phase at –20°C to the liquid phase at 50°C.

b) For each of the following processes or reactions, circle the appropriate choice to indicate whether ∆H for the process or reaction is less than or greater than zero.

i) H2 (g) + ½ O2 (g) à H2O (l)

∆H < 0 ∆H > 0 (circle one)

ii) H2O (g) à H2O (l)

∆H < 0 . ∆H > 0 (circle one)

iii) In an instant ice pack, ammonium nitrate dissolves in water and the resulting solution becomes very cold. For the following process: NH4NO3 (s) à NH4NO3 (aq)

∆H < 0 ∆H > 0 (circle one)

c) For each of the following statements, circle True or False to indicate whether or not the statement is correct.

i) True or False --> If a reaction produces oxygen gas as the only gaseous product and the oxygen gas is collected over water, then the partial pressure of oxygen gas collected is equal to the total pressure plus the vapor pressure of water.

ii) True or False --> If the following reaction occurs in a rigid sealed vessel at constant temperature, the total pressure in the vessel will remain constant: H2 (g) + I2 (g) à 2 HI (g)

iii) True or False --> n a sample of nitrogen gas at 25°C, all of the nitrogen gas molecules are moving at a speed equal to uRMS.

Answer 1

latent heat of fusion of ice = 334J/g

a) First stage   Heat content , Q required to heat ice at -20^oC to 0^oC = m x c dt

m= 36 g (mass of ice , c = specific heat of ice = 2.09 j/^oC . g , dt = [0^oC- (-20^oC )

Q = 36 g x 2.087 j/^oC . g x [0^oC- (-20^oC )

= 1502.64 joules.

PHASE change (second stage)

Heat content)Q) required to convert 36 g of ice at 0^oC to liquid water at 0^oC --------

Q = mass x latent heat of fusion of ice.

= 36 g x 334J/g

= 12024 J

Third statge

Heating water at zero celsius to water at 25^oC , Q = m x c x dt

= 36 g x 4.18 j/^oC . g x [50^oC- 0^oC]

= 7524 Joules

Total heat content required to change 36 grams of ice (H2O (s)) from the solid phase at –20°C to the liquid phase at 50°C.= sum of heat quantities in all the three stages---

= 1502.64 joules. + 12024 J + 7524 Joules

= 21050.6 joules

= 21.051 KJ

b) (i) for the reaction H2 (g) + ½ O2 (g)---------------> à H2O (l) , the enthalpy would be less than zero

since it is condensation the energy is released, so H < 0

(ii) ii) H2O (g)------------------------> à H2O (l) This is condensation and so energy is given out

so H < 0

(iii) For NH4NO3 (s) --------------------------------- > NH4NO3 (aq) .

For the above dissolution process energy is absorbed by system , NH4NO3 (s) .

so H > 0

C)(i) False- The partial pressure of the oxygen gas = total pressure - vapour pressure of water.

(ii) true -- since the number of moles of reactants( total 2) equals number of moles of products (2)

H2 (g) + I2 (g) -----------------------------> 2 HI (g)

(iii) true -- since the root mean square velocity is the velocity of all molecules having same kinetic energy which equals the kinetic energy of sample of the nitrogen( only gas) at the given temperature.