# Calorimetry and Hess' Law

Detailed work would be very helpful; the math involved in this gets me confused, but I'm not sure where I have been going wrong. If work is handwritten, please do not write in cursive for I have problems reading it.

1. The mass of a substance is 200gm and its specific heat is 0.09. How much heat is required to raise the temperature of the substance from 20°C to 90°C?

2. The heat capacities of mercury and glass are the same. The density of mercury is 13.6gm/cc and the density of glass is 2.5gm/cc. If the specific heat of mercury is 0.03, what will be the specific heat of glass?

3. A body of mass 100gm is heated to 122° C and then quickly dropped into a copper calorimeter of mass 50gm. The calorimeter contains 300gm of water at 28° C. The final temperature of the system becomes 30° C. What is the specific heat of the body if the specific of copper is 0.09?

4. Use the following information to determine the enthalpy (?H°) of the reaction for:

NO2 (g) + (7/2) H2 (g) --> 2H2O (l) + NH3 (g)

Using the following two equations:

2NH3 (g) --> N2 (g) + 3H2 (g) ?H° = +92 kJ

(1/2) N2 (g) + 2H2O (l) --> NO2 (g) + 2H2 (g) ?H° = +170kJ

5. The compound carbon suboxide, C3O2, is a gas at room temperature. Use the data supplied the calculate the heat of formation of carbon suboxide.

2CO (g) + C (s) --> C3O2 (g) ?H° = +127.3 kJ

CO(g) ?H° = -110.5 kJ

https://brainmass.com/chemistry/hess-law/calorimetry-hess-law-519022

#### Solution Preview

1. The mass of a substance is 200gm and its specific heat is 0.09. How much heat is required to raise the temperature of the substance from 20° C to 90° C?

If the unit for specific heat is cal/(gm0C), unit for the mass is gm and unit for ∆T is 0C.

Therefore, Q=mS∆T=200*0.09*(90-20)=1260 cal (units of gm and 0C have been canceled out).

2. The heat capacities of mercury and glass are the same. The density of mercury is 13.6gm/cc and the density of glass is 2.5gm/cc. If the specific heat of mercury is 0.03, what will be the specific heat of glass?

Assume V is the volume for mercury and glass, s is the specific heat for glass.

Then the ...

#### Solution Summary

The expert examines calorimetry and Hess' law.

Hess's Law of Heat Summation

When 39.5 mL of 0.525 M (H4)(SO4) is added to 39.5 mL of 1.05 M KOH in a coffee-cup calorimeter at at 23.50 C, the temperature rises to 30.17 C. Calculate the H of this reaction (Assume that the total volume is the sum of the individual volumes and that the density and specific heat capacity of the solution are the same as for pure water).

"Delta H per mole of H2SO4 = ?

"Delta H per mole of KOH = ?