The disaccharide milk sugar lactose can be hydrolyzed to glucose and galactose u

Question

The disaccharide milk sugar lactose can be hydrolyzed to glucose and galactose using the enzyme lactase or P-galactoisedase. The reaction is written as

Lactose (aq) + H2O (liq) ---> Glucose (aq) + Galactose (aq)

Calorimetric analysis of the reaction indicates that the heat of reaction at 298 K is 0.44 kJ/mol. Also (delta)Cp for the reaction is 9 J/mol.K.

(A) At 298 K, heat of formation of glucose is -1262.19 kJ/mol, and lactose is -2233.08 kJ/mol. What is the heat of formation of galactose?

(B) If the reaction is carried out using 300 moles of Lactose at 37 C, determine the change in enthalpy.

Explanation / Answer

(A)

Heat of formation of H20 liq = -286 kJ/mol

Heat of reaction = heat of formation of products - heats of formation of reactants

0.44 kJ/mol = ( H of glucose + H of galactose ) - ( H of Lactose + H of water )

0.44 kJ/mol = ( -1262.19 kJ/mol + H of galactose ) - ( -2233.08 kJ/mol - 286 kJ/mol )

H of galactose = -1257.33 kJ/mol

(B)

delta H = mC(T2 -T1)

= 300 moles x 9 J/mol K x ( 310 - 298 )

=32.4 kJ

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