Enthalpy

background [prelab assignment (20 points) due at the beginning of the lab]

This laboratory activity is based on investigation 12 in your AP chemistry lab manual; thus, it provides some relevant background for the following prelab questions and this laboratory activity.

based on the description in Procedure / part 2 & the remainder of the chapter in investigation 12 in the AP chemistry lab manual, describe / rationalize the calculation to determine the calorimeter's heat capacity (the lab manual uses the term, "calorimeter's constant", instead of heat capacity). There is a difference between heat capacity and specific heat.

design / describe an experimental protocol to determine the heat of fusion of ice

Using Hess' law, what is the relationship between the below reactions ?

dissolve solid NaOH in HCl solution

dissolve solid NaOH in water

mix NaOH solution & HCl solution

sketch a data table for this lab containing entries for all required experimental measurements [i.e. review purpose & content of lab report]

purpose

experimentally, determine the heat of fusion of ice

experimentally, determine ΔH

dissolve solid NaOH in water,  i.e. NaOH(s) -> NaOH(aq) [or Na+(aq) + OH-(aq)]

dissolve solid NaOH in a HCl solution,  i.e. NaOH(s) + HCl(aq) -> H2O + NaCl(aq)

using the above information, determine the change in enthalpy to mix NaOH & HCl solutions,  i.e. NaOH(aq) + HCl(aq) -> products

compare experimental versus theoretical ΔH using statistics

determine the calorimeter's heat capacity

materials

NaOH, HCl, water, ice

coffee cup; thermometer

balance; hot plate

methods [delegate lab work]

heat of fusion of ice:  student design  [use an amount of water & ice, such that the final temperature is between 5 - 15 °C]

Δ H to dissolve solid NaOH in water: add ~2 g NaOH to 50 mL water

Δ H to dissolve solid NaOH in HCl solution: add ~2 g NaOH to 50 mL 2 .0 M HCl

determine the calormeter's heat capacity (student design), where the total volume of added water ~ 50 mL

data analysis

student design

 

Content of lab report [60 points]

data analysis 

data table(s) of your experimental measurements [5 points]

based on your group's data and ignore the calorimeter's heat capacity, determination of the experimental values of ΔH of the below reactions (express on a mole basis) [20 points]

experimental determination of the calorimeter's heat capacity [5 points]

include calorimeter's heat capacity in calculation of __ (10 points)

determination of the theoretical  value of the ΔH to dissolve solid NaOH in water (5 points)

statistical analysis (include interpretation of p-value) of class data; effect of including calorimeter's heat capacity in the determination of __ (10 points)

ΔHfusion

dissolve solid NaOH in water

conclusion: importance of including the calorimeter's heat capacity in your calculations; support your conclusion. (5 points)

selected links

Hess's law problems

calorimeter use

lab activity source (examples):  site 1  & site 2 [access 4 / 2009]