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Unformatted text preview: Title: Calorimetry and Hesss Law Course: Chemistry 118 Date: January 22, 2008 INTRODUCTION In this lab, we were to use concepts of calorimetry and Hesss law to determine H. H, change in enthalpy of the reaction, is the change in the heat content of a chemical system during a reaction. It equals the amount of heat that the reaction absorbs in constant pressure (H=q p ). When H is positive, we call the reaction endothermic, which represents that the heat flows into the system. Oppositely, when H is negative, we call the reaction exothermic, which the heat flows to the surroundings. We can find H not only by performing an actual experiment, but also by using theoretical values. We can use tables of H f , standard enthalpy changes, using the equation, H(reaction) = H f (products) - H f (reactants). The H of any reaction can be calculated using sets of balanced chemical equations and tabulated values of Hf. It is stated in Hesss law that the amount of heat absorbed in a reaction at constant pressure is the same regardless of whether the reaction occurs in a single step. PROCEDURE 1) construction of a calorimeter a. obtain 5 x 5 square inch of cardboard, rubber band, and 250mL beaker b. make a hole in the center of cardboard c. pass the thermometer through d. place this set-up inside one of the metal cans 2) heat capacity of the calorimeter a. measure 50mL of de-ionized water in a graduated cylinder b. pour it into the inner beaker c. close the calorimeter and stir d. take temperature readings to 0.1C every 20-30 seconds until no further temperature change is observed e. record the temperature initial temperature of the cool water f. replace the calorimeter lid g. place 50mL of de-ionized water in a beaker and heat it until 10 to 15C hotter than the water in the calorimeter h. stir and measure temperature i. record the temperature initial temperature of the warm water j. pour warm water into the calorimeter k. swirl the mixture and take temperature readings every 20-30 seconds until no temperature change (take 2-3 minutes) l. record the maximum temperature of the system m. repeat for two trials 3) Enthalpy of neutralization a. add 50mL of 2.00M HCl to the calorimeter b. place 50mL of 2.00M NaOH in a beakerplace 50mL of 2....
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