Lab 2 Enthalpy Change Lab Assignment F18

Lab 2 Assignment: Enthalpy Change of a Chemical Reaction In this part of the lab, you measured the temperature changes of hot and cold water before and after mixing in a calorimeter. This allows you to determine the heat capacity of the calorimeter using the law of conservation of energy. The heat capacity of the calorimeter tells us the relationship between the heat change of the calorimeter and the temperature change of the calorimeter, and has units of J/°C. Be sure to record all data and calculated results with the correct number of significant figures . Experiment 1: Determining the Heat Capacity of the Calorimeter 1. Record the following measured data.  When recording data , remember to record all numerical digits displayed by the measuring device. Measurement Trial 1 Trial 2 Trial 3 a Initial temperature of the cold water in the calorimeter (°C): 21.5 ℃ 21.5 ℃ 21.5 ℃ b Initial temperature of the hot water (°C): 60.0 ℃ 60.0 ℃ 60.0 ℃ c Mass of the hot water (g) (assume density of 1.00 g/mL) 50g 50g 50g d Mass of the cold water (g) (assume density of 1.00 g/mL) 50g 50g 50g e Final (maximum) temperature of water mixture the calorimeter (°C): 40.2 ℃ 40.2 ℃ 40.2 ℃ 2. Record calculated values.  In the following table, record calculated values for the designated temperature changes and heat changes of the hot and cold water, and then use those values to calculate the heat change of the calorimeter using the law of conservation of energy. Note that the final temperature is the temperature of the mixture of hot and cold water.  When reporting a calculated value, follow the significant figure rules reported so that precision is correct. (Detailed rules for significant figures are in Activity 1.) o When adding and subtracting, retain the number of decimal places equal to the least number of decimal places in the values used in the calculation. o When multiplying and dividing, retain the number of significant figures equal to the least number of significant figures in the values used in the calculation. o When doing a multi-step calculation, it’s good practice to retain a couple extra significant figures until the final answer, but record the correct number of significant figures when asked to report intermediate answers.

Calculated Value Trial 1 Trial 2 Trial 3 f Calculate change in Temperature,  T hot water ( T final – T initial hot ) -19.8 ℃ -19.8 ℃ -19.8 ℃ g Calculate change in temperature,  T cold water ( T final – T initial cold ) 18.7 ℃ 18.7 ℃ 18.7 ℃ h Calculate q hot (J) (Use specific heat equation) -4144.14J -4144.14J -4144.14J j Calculate q cold (J) (Use specific heat equation) +3913.91J +3913.91J +3913.91J k Calculate q calorimeter (J) (Use equation for Law of Conservation of Energy) 230.23J 230.23J 230.23J l Calculate Heat Capacity of Calorimeter, C p (J/°C) (from q calorimeter and  T calorimeter ) 12.31J/ ℃ 12.31J/ ℃ 12.31J/ ℃ m Average Heat Capacity of Calorimeter, C p , J/°C) 12.31J/ ℃ 3. Show your calculations with results for the Trial 1 values in the indicated table rows in the previous question. Be sure to include units and record all calculated results with the correct number of significant figures . f Show your work: T ❑ final − T initial = 40.2 − 60.0 = 19.8 ℃ g Show your work: T ❑ final − T initial = 40.2 − 21.5 = 18.7 ℃ h Show your work: q hot = ( 4.186 J g ℃ ) ( 50 g ) ( − 19.8 ℃ ) =− 4144.14 J j Show your work: q cold = ( 4.186 J g ℃ ) ( 50 g ) ( 18.7 ℃ ) = 3913.91 J k Show your work: q calorimeter = 4144.14 J − 3913.91 J = 230.23 J l Show your work: Calorimeter capacity = 230.23 J 18.7 ℃ = 12.31 J / ℃