Question

16. Given the following reactions 

CaCO3 (s) → CaO (s) + CO2 (g) ΔH°=178.1 kJ 

C(s, graphite) + O2 (g) → CO2 (g) ΔH°=-393.5 k 

According to Hess's Law, what is the enthalpy of the reaction (k) for 

CaCO3(s) → CaO (s)+C(s. graphite) +O2(g)? 

-571.6 

-215.4 

5716 

215.4 

701.2 

Question 17 

According to the definition of standard enthalpy of formation, ΔH°, which of the following's ΔH° is zero? 

Question 18

Given the data in the table below, calculate the ΔH°rxn (kJ) for the reaction 

4NH3(g)+5O2 (g) → 4NO (g)+6H2O (I) 

Answer 1

16)

Lets number the reaction as 1, 2, 3 from top to bottom

required reaction should be written in terms of other reaction

This is Hess Law

required reaction can be written as:

reaction 3 = +1 * (reaction 1) -1 * (reaction 2)

So, ΔHo rxn for required reaction will be:

ΔHo rxn = +1 * ΔHo rxn(reaction 1) -1 * ΔHo rxn(reaction 2)

= +1 * (178.1) -1 * (-393.5)

= 571.6 KJ

Answer: 571.6 KJ

17)

ΔHof is 0 for elements in their standard state

OH- is compound of Oxygen and hydrogen

Hg(l) is standard state of mercury

Al(s) is in standard state. So, ΔHof is 0

NaCl is compound of sodium and chlorine

He(g) is standard state of Helium

Answer: Al(s)

Only 1 question at a time please