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Partners: Jeff Somvorachith, Connor Engels 
 10. Additivity of Heats of Reaction: Hess's Law 
 Purpose: 
 To practice applying Hess's Law using a coffee cup calorimeter and confirming that the heat of one reaction should be equal to the sum of the heats for the other reactions. 
 Pre-Lab: 
 (1) Na + (aq) + OH - (aq) --> NaOH (s) 

 -ΔH 1 
 (2) NaOH (s) + H + (aq) + Cl - (aq) --> H 2 O (l) + Na + (aq) +Cl - (aq)   ΔH 2 
 (3) Na + (aq) + OH - (aq) + H + (aq) + Cl - (aq) --> H 2 O (l) + Na + (aq) +Cl - (aq)   ΔH 3 
 Procedure: 
 
 
 
 Wear protective equipment. 
 Open Vernier Graphical Analysis. Connect the temperature probe.  
 Use a utility clamp and a slit stopper to suspend the temperature probe from a ring stand. 
 Place a Styrofoam cup into a 250mL beaker. Measure out 100.0mL of distilled water into the cup. Lower the temperature probe into the solution. 
 Weigh out around 2 grams of solid sodium hydroxide and record the mass to the nearest 0.01g. 
 Begin collecting data and obtain the initial temperature, t 1 . After obtaining the initial temperature, add the NaOH to the cup. Stir continuously until the temperature has maximize and has begun to drop. Record the maximum temperature, t 2 . After 3.3-4 minutes, data collection is completed. 
 Graph temperature vs. time(done automatically). Examine the data points along the curve to verify the values of t 1 and t 2 .