Question

Calculate the amount of heat required to completely sublime 28.0 g of solid dry ice (co2 at its sublimation temperature. the heat of sublimation for carbon dioxide is 32.3 kj/mol.

Answer 1

Answer : The amount of heat required to complete sublime of $CO_2$ is 20.5 kJ.

Explanation :

First we have to calculate the moles of $CO_2$.

$\text{ Moles of }CO_2=\frac{\text{ Mass of }CO_2}{\text{ Molar mass of }CO_2}=\frac{28.0g}{44g/mole}=0.636moles$

Now we have to calculate the amount of heat required to complete sublime of $CO_2$.

As, 1 mole of $CO_2$ on sublimation required heat = 32.3 kJ

So, 0.636 mole of $CO_2$ on sublimation required heat = 0.636 × 32.3 kJ = 20.5 kJ

Therefore, the amount of heat required to complete sublime of $CO_2$ is 20.5 kJ.

Answer 2

 There is no need to do anything about the temperature, because sublimation does not involve any temperature change.

First, determine how many moles of CO2 there are. The mol. wt. of CO2 is 12 +2 x 16 = 44 g/mol. 

So, 25.0 equals 25/44 = 0.568 moles

So the heat required is 0.568 mol x 32.3 KJ/mol = 18.3