Ch 5 Calorimetry Calorimetry vocabulary n Calorimetry the

Ch 5: Calorimetry

Calorimetry (vocabulary) n Calorimetry- the measurement of heat flow n n Heat Capacity (C)- heat required to raise the temp of a substance by 1 K n n n A Calorimeter is an instrument that measures heat flow Units for C are J/K Molar Heat Capacity (Cmolar) – heat absorbed by 1 mole of a substance when its temp changes 1 K n Units are J/mol*K Specific Heat Capacity- heat capacity of one gram of a substance. Units are J/g*K n For Water it is 4. 184 J/g*K or 1. 00 cal/g*K

Calorimeter n Rxns at constant pressure can be studied using a calorimeter (Styrofoam cup) n n If heat is evolved (released) by rxn, temp of solution increases. If heat is absorbed, temp of solution decreases Since mass of solution is known, heat (q) can be calculated using q = m. CΔT

Using Specific Heat (spht) to calc. Heat Change The spht of ammonia is 4. 381 J/g*K. Calculate the heat required to raise the temp of 1. 50 g of ammonia from 213. 0 K to 218. 0 K. 1. 2. 3. q = m. CΔT q = (1. 50 g)(4. 381 J/g*K)(5. 0 K) q = 33 J

Calculating Heat of Combustion 0. 800 g of S is combusted to form SO 2. All of the heat evolved is used to raise the temp of 100. 0 g of water by 17. 8 K. (a) Write the rxn for the heat of combustion of sulfur (b) Calculate the heat of combustion of 1 mole of sulfur

Calculating Heat of Combustion a) b) S(s) + O 2(g) SO 2(g) q = m. CΔT q = (100. 0 g)(4. 184 J/g*K)(17. 8 K) q = 7450 J This is the heat of combustion when. 800 g of S reacts with O 2. Covert g of S to mol of S to determine the J per mol. . 800 g S / (32. 0 g/mol) =. 025 mol of S 7450 J /. 025 mol = 298000 J/mol = 298 k. J/mol

For HW, read Section 5. 6 “Hess’s Law” n n This is what happens to me when my daddy tries to teach me chemistry I’ll be in to visit you guys tomorrow!!!