thermochemistry-with solutions

thermochemistry-with solutions - Osukuuni Practice...

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Osukuuni Practice Questions CHEM 1211 Thermochemistry 1. Classify the following processes as exothermic or endothermic: (a) freezing of water (b) melting of ice (c) boiling of water (d) heating with a furnace (a) exothermic (b) endothermic (c) endothermic (d) exothermic 2. Is the specific heat of a substance intensive or extensive property? Explain Specific heat capacity is J/g.K. It is constant for any given substance and does not depend on the amount of substance, hence intensive property. Note that heat capacity (J/K), on the other hand, depends on the mass of substance and is extensive (heat capacity = mass x specific heat capacity) 3. Calculate q when 0.20 g of ice is cooled from 10 o C to -75 o C (C ice = 2.087 J/g.K). q = C s x m x T = (2.087 J/g.K) x (0.20 g) x (-75 - 10) = -35 J 4. A 325-g aluminum engine part at an initial temperature of 3.00 o C absorbs 85.0 kJ of heat. What is the final temperature of the part (C Al = 0.900 J/g.K)? q = C s x m x T ( 29 ( 29 C 3.00 T x g) (325 x J/g.K 0.900 kJ 1 J 1000 x kJ 85 o 2 - = T 2 = 294 o C 5. One piece of copper jewelry at 120 o C has exactly twice the mass of another piece, which is at 52 o C. Find the final temperature inside the calorimeter if both pieces are placed in the calorimeter. (Assume calorimeter has negligible heat capacity; C copper = 0.387 J/g.K) If mass of copper at 52 o C = m, then mass of copper at 120 o C = 2m q hot = - (q cold + q cal ) q hot copper = C s x m x T = C s x 2m x (T 2 - 120 o C) q cold copper = C s x m x T = C s x m x (T 2 - 52 o C) Negligible heat capacity of calorimeter implies q cal = 0 and q hot = - q cold C s x 2m x (T 2 - 120 o C) = - [C s x m x (T 2 - 52 o C)] C s and m are found on both sides so they cancel 2 x (T 2 - 120 o C) = - (T 2 - 52 o C) T 2 = 97 o C
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6. An unknown volume of water at 18.2 o C is added to 24.4 mL of water at 35.0 o C. If the final temperature is 23.5 o C, what is the unknown volume? (Assume that no heat is lost to the surroundings; density of water is 1.00 g/ml)
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thermochemistry-with solutions - Osukuuni Practice...

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