The heat of reaction of both the reactions 2 KOH H2SO4 → K2SO4 2H2...
Given:
The heat of reaction for the reactions:
1) 2 KOH + H2SO4 → K2SO4 + 2 H2O
2) Mg(OH)2 + H2SO4 → MgSO4 + 2 H2O
is -27.2 kcal/mol.
To find:
The heat of reaction for the reaction:
3 Ca(OH)2 + 2 H3PO4 → Ca3(PO4)2 + 6 H2O
Solution:
The heat of reaction is a measure of the energy released or absorbed during a chemical reaction. It can be calculated using the principle of Hess's law, which states that the overall enthalpy change in a reaction is independent of the pathway taken.
Hess's Law:
Hess's Law states that if a reaction can be expressed as the sum of two or more reactions, then the heat of reaction for the overall reaction is equal to the sum of the heats of reaction for the individual reactions.
Step 1: Equation 1: 2 KOH + H2SO4 → K2SO4 + 2 H2O
The heat of reaction for this equation is -27.2 kcal/mol.
Step 2: Equation 2: Mg(OH)2 + H2SO4 → MgSO4 + 2 H2O
The heat of reaction for this equation is also -27.2 kcal/mol.
Step 3: Equation 3: 3 Ca(OH)2 + 2 H3PO4 → Ca3(PO4)2 + 6 H2O
To find the heat of reaction for this equation, we can use Hess's Law.
Step 4: We can rewrite equation 3 as the sum of equations 1 and 2:
3 Ca(OH)2 + 2 H3PO4 → Ca3(PO4)2 + 6 H2O
= 3(2 KOH + H2SO4) + 2( Mg(OH)2 + H2SO4) → Ca3(PO4)2 + 6 H2O
Step 5: Applying Hess's Law, the heat of reaction for equation 3 is the sum of the heats of reaction for equations 1 and 2:
Heat of reaction for equation 3 = 3(Heat of reaction for equation 1) + 2(Heat of reaction for equation 2)
= 3(-27.2 kcal/mol) + 2(-27.2 kcal/mol)
= -81.6 kcal/mol
Answer:
The heat of reaction for the reaction 3 Ca(OH)2 + 2 H3PO4 → Ca3(PO4)2 + 6 H2O is -81.6 kcal/mol. Therefore, option (C) -81.6 kcal/mol is the correct answer.
The heat of reaction of both the reactions 2 KOH H2SO4 → K2SO4 2H2...
Option C.....-81.6kcal/mol.