Do Now Answer these in your notes: Draw a coffee cup calorimeter in your notes. How do we use a coffee cup calorimeter? When looking at q (heat) how can we tell is a value is endothermic or exothermic?

Exothermic A reaction that is exothermic gives off heat and the change in enthalpy is negative (ΔH° < 0). The temperature of the surroundings increases during an exothermic process. Copyright © Cengage Learning. All rights reserved

Endothermic A reaction that is endothermic absorbs heat and the change in enthalpy is positive (ΔH° > 0). The temperature of the surroundings decreases in an endothermic process. Copyright © Cengage Learning. All rights reserved

A Coffee–Cup Calorimeter Made of Two Styrofoam Cups Copyright © Cengage Learning. All rights reserved

Calorimetry Calorimetry is the measurement of heat flow. It allows us to calculate the amount of energy required to heat up a substance or to make a substance change states.

Direction of Heat Flow Surroundings ENDOthermic EXOthermic qsys > 0 System ENDOthermic qsys > 0 EXOthermic qsys < 0 System H2O(s) + heat  H2O(l) melting H2O(l)  H2O(s) + heat freezing Kotz, Purcell, Chemistry & Chemical Reactivity 1991, page 207

Experimental Determination of Specific Heat of a Metal Typical apparatus used in this activity include a boiler (such as large glass beaker), a heat source (Bunsen burner or hot plate), a stand or tripod for the boiler, a calorimeter, thermometers, samples (typically samples of copper, aluminum, zinc, tin, or lead), tongs (or forceps or string) to handle samples, and a balance.

A Coffee Cup Calorimeter Thermometer Styrofoam cover cups Stirrer A Coffee Cup Calorimeter Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 302

Calorimetry Energy released (heat) = m × c × ΔT s (sometimes c) = specific heat capacity (J/°C·g) m = mass (g) ΔT = change in temperature (°C) Copyright © Cengage Learning. All rights reserved

Calorimetry Coffee Cup Calorimetry Experimental way of measuring heat generation/consumption by essentially catching all the heat energy in a water bath or water bath + metal apparatus. Coffee Cup Calorimetry Styrofoam cup insulates the contents so any heat generated or consumed in the water can be measured by the temperature change -qmetal = mCH2O∆T

Calorimetry Surroundings SYSTEM Tfinal = 26.7oC “loses” heat H2O Ag m = 75 g T = 25oC m = 30 g T = 100oC

- [(sFe) (mFe) (DTFe)] = (Swater) (mwater) (DTwater) 240 g of water (initially at 20oC) are mixed with an unknown mass of iron (initially at 500oC). When thermal equilibrium is reached, the system has a temperature of 42oC. Find the mass of the iron. Fe T = 500oC mass = ? grams s = 0.45 J/goC T = 20oC mass = 240 g -qFe= qwater - [(sFe) (mFe) (DTFe)] = (Swater) (mwater) (DTwater) mFe = 107.3 g Fe Calorimetry Problems 2 question #5

- [(sAu) (mAu) (DTAu)] = (Swater) (mwater) (DTwater) A 97 g sample of gold at 785oC is dropped into 323 g of water, which has an initial temperature of 15oC. If gold has a specific heat of 0.129J/goC, what is the final temperature of the mixture? Assume that the gold experiences no change in state of matter. Au T = 785oC mass = 97 g T = 15oC mass = 323 g -qAu= qwater - [(sAu) (mAu) (DTAu)] = (Swater) (mwater) (DTwater) - [(0.129 J/goC) (97 g) (Tf - 785oC)] = (4.184 J/goC) (323 g) (Tf - 15oC)] Tf = 22.1oC Calorimetry Problems 2 question #8

A 322 g sample of lead (specific heat = 0 A 322 g sample of lead (specific heat = 0.138 J/goC) is placed into 264 g of water at 25oC. If the system's final temperature is 46oC, what was the initial temperature of the lead? T = ? oC Pb mass = 322 g Ti = 25oC mass = 264 g Pb Tf = 46oC -qPb= qwater - [(sPb) (mPb) (DTPb)] = (Swater) (mwater) (DTwater) - [(0.138 J/goC) (322 g) (46oC - Ti)] = (4.184 J/goC) (264 g) (46oC- 25oC)] Ti = 568oC Calorimetry Problems 2 question #12