A substance X has the following properties Calculate the ene

A substance, X, has the following properties. Calculate the energy that must be removed to convert 250. grams of the substance X from a gas at 120.degree C to a solid -46.0 degree C. Assume X has a molar mass of 75.0 g/mol. kJ

Solution

Try to estimate energy needed to cool X-vapor from 120ºC to its condensation temp of -46ºC
250g x (120º-75 C) x 1.0J/gC = 112500J =

11.25KJ

Now estimate to condense 250g of X-vapor at 75 C to X-liquid at 75C:

20.0kJ/mol x (250g/75g/mole) =

66.66kJ

Now estimate energy to cool 250g of liquid X from 75 C to its freezing point of -15C
250g x (75º -(-15º)C) x 2.5J/gC =56250J =

56.25KJ

Then try to convert 250 g of liquid X at -15 º C to solid X at -15 º C:

5.0kJ/mol X (250g/75g/mol) =

16.66KJ

Finally cool the 250g of solid X from -15 º C to -46 º C:

250g x (-15º -(-46º))C x 3.0J/gC = 23250J =

23.25KJ

=174.2 KJ

we need 174.2 KJ of energy needs to be removed to convert 250 grams of the substance X from a gas at 120ºC to a solid -46ºC.

Try to estimate energy needed to cool X-vapor from 120ºC to its condensation temp of -46ºC 250g x (120º-75 C) x 1.0J/gC = 112500J =	11.25KJ
Now estimate to condense 250g of X-vapor at 75 C to X-liquid at 75C: 20.0kJ/mol x (250g/75g/mole) =	66.66kJ
Now estimate energy to cool 250g of liquid X from 75 C to its freezing point of -15C 250g x (75º -(-15º)C) x 2.5J/gC =56250J =	56.25KJ
Then try to convert 250 g of liquid X at -15 º C to solid X at -15 º C: 5.0kJ/mol X (250g/75g/mol) =	16.66KJ
Finally cool the 250g of solid X from -15 º C to -46 º C: 250g x (-15º -(-46º))C x 3.0J/gC = 23250J =	23.25KJ
	=174.2 KJ