Thermodynamics, Enthalpy of Reaction Lab

Topics: Enthalpy, Energy, Thermodynamics Pages: 3 (735 words) Published: May 15, 2014
Name
Lab Partner Name(s)
Thermodynamics, Enthalpy of Reaction Lab
March 27, 2014

I. Purpose

The purpose of this lab is to learn how to determine the heat of reaction.

II. Safety

1. Wear appropriate safety attire (goggles, aprons, hair tie, etc.). 2. Do not directly inhale or ingest chemicals.
3. Understand safety information regarding the chemicals being handled during the lab (hydrochloric acid, sodium hydroxide). 4. Be aware of how to operate all lab equipment.
5. Clean hands and experimentation area before exiting the lab. 6. Listen for any additional direction from the instructor.

III. Pre-lab Questions

1. Define ΔHrxn.
ΔHrxn is enthalpy of products – reactants. (ΔHrxn = Hprod-Hreact). 2. In today’s lab you will be using 50.0 mL of 2.0 M HCl. Using Equation 3 (M=mol/L) from above, calculate the number of moles of acid used.

M=mol/L  2.0M = x / 0.0500L  x = 0.10 mol HCl
3. You will also be using 50.0 mL of 2.0 M NaOH. How many moles of base are used?
M=mol/L  2.0M = x / 0.0500L  x = 0.10 mol NaOH
4. The specific heat of a solution is 4.18 J/g ºC. The solution is formed by combining 25.0 g of solution A with 25.0 g of solution B, with each solution initially at 21.4ºC. The final temperature of the combined solutions is 25.3ºC. Calculate the qsol using equation 1 (qsol = grams of solution x specific heat of solution x ΔT). Answer in kJ.

q = mCΔT  q = (50.09)(4.18J/g ºC)(3.9ºC)  0.82kJ
5. What is the qrnx ?
-qsol = qrnx  -0.82 kJ
6. If the reaction described in #4 used 0.15 moles of B, calculate ΔHrxn by dividing kJ by moles.
ΔHrxn = -0.82 kJ / 0.15 mol  ΔHrxn = -5.5 kJ/mol

IV. Procedures

Measure 50.0 mL of a 2.0 M HCl solution in a graduated cylinder prior to transferring to the calorimeter, making sure to record the temperature of the HCl solution in the data table. Then, rinse the graduated cylinder with distilled water before measuring 50.0 mL of a 2.0 M NaOH solution, making sure to record the...
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