Apply Hess\'s Law to solve the following problems with the information given. Fi

Question

Apply Hess's Law to solve the following problems with the information given. Find the enthalpy change for the vaporization of 2 moles of water. Find the enthalpy change for the vaporization of 1 mole of water. How much energy is needed to "sublime" 18 g of ice to vapor? Consider this reaction: What is the value of delta H if the equation is multiplied throughout by 2? What is the value of delta H if the direction of the reaction is reversed so that the products become the reactants and vice versa? What is the value of delta H if water vapor is formed instead of liquid water as the product? (You may need to use data found in Question 1 above)

Explanation / Answer

Q1.

a)

vaporization for 2 mol...

use

H2O(s) --> H2O(l)

CH4 + 2O2 = CO2 + 2H2O(l)

cH4 + 2O2 = CO2 + 2H2O(g)

we need H2O (g) in the right, so invert (2) and multiply (1) by 2:

2H2O(s) --> 2H2O(l) H = 6.01*2

CO2 + 2H2O(l) = CH4 + 2O2 H = 890.4

CH4 + 2O2 = CO2 + 2H2O(g) H= -802.4

Add 2 and 3

= H = 890.4

CO2 + 2H2O(l) + CH4 + 2O2 = CO2 + 2H2O(g) + CH4 + 2O2 H= -802.4+ 890.4

2H2O(l) = 2H2O(g) H = 88 kJ/mol

for 1 mol:

88/2 = 44 kJ/mol

c

for sublimation..

add all2H2O(l) = H2O(g) H = 44 kJ/mol

H2O(s) --> H2O(l) H = 6.01

HRxn = 44+6.01 = 50.01 kJ/mol

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