Question

1127 Chapter 6 Discussion Problems 1. How much energy must be transferred to raise the temperature of a cup of coffee (250 mL) from 20.5°C 10 95.6°C? Assume density and specific heat is the same as Water 4.16 Ig/ml 2. An 38.5 g piece of iron with temperature 78.8°C is placed in a beaker containing 244 g of water at 18.8°C. When thermal equilibrium is reached, what is the final temperature? Assume no energy loss to the surroundings. 3. Sucrose C H .0, can be oxidized to CD, and H.O. The enthalpy change for the reaction is given by AH What is the energy transferred as heat by burning 5.00 g of sucrose? CH..0 (s) + 120, (B) - 1200, (g) +11H.0 (1) AH = -5645 kJ/mol 4. You are given the following thermochemical equation. Find the enthalpy of CIF, (g). Round your answer to the nearest whole number. 2CIF, (s) + 2NH (8) - N, (B) + 6HF (8) + Cl (8) AH -1196 kJ Compound AH" (kJ/mol) Compound AH (kJ/mol) NO. (8) 35 HCI (8) -92 307 NH (9) 46 HF (g) -273.3 HO (8) -241.82 H.O() -187.78 5. Calculate the enthalpy of formation of CH (8) if AH',for CO(g) is -393.5 kJ/mol and AH", for HO ) is-242 l/mol. 2CH (8) 50(8) -- 4C0() + 2H,0 (B) AH = -3514

The specific heat of iron is 0.450 J/g°C

Answer 1

Ans 1 :

Heat = mass x specific heat x change in temperature

here mass of coffee :

= density x volume

= 250 mL x 1 g/mL = 250 g

specific heat = 4.18 J/g^oC

so putting values :

heat = 250 g x 4.18 J/g^oC x (95.6^oC - 20.5^oC)

= 78479.5 J

so 78479.5 Joules of energy is required