Hess's Law Lab Report

Hess’s Law Lab

Ms. Manal Abi Saab

Marwan Kassar

Chemistry SL IB A

Data collection and Processing:
This is a sample schematic diagram for a coffee cup calorimeter for Route 1:

KOH(aq) solution
KOH(aq) solution

In this lab we will attempt to prove Hess’s Law. Hess’s Law states that if two or more thermochemical equations are combined to produce a final equation for a reaction, then the sum of the enthalpy changes for the individual reactions is the enthalpy change for a final reaction. It is very difficult to calculate the enthalpy change of some reactions such as KOH(s) + HCl(aq) → KCl(aq) + H2O(l) and so Hess’s Law attempts to calculate the enthalpy change of the reaction stated previously ∆H1 by performing 2 other reactions. The first reaction to be studied is KOH(s)→ KOH(aq) having an enthalpy change of ∆H2 and KOH(aq) + HCl(aq) → KCl(aq)+ H2O(l) having an enthalpy change of ∆H3. For Hess’s Law to be verified, ∆H1 should be = ∆H2+ ∆H3.

Collecting Raw Data:
Table 1: Qualitative Raw Data
Route Taken | Qualitative Observation |
    * Route 1 |     * HCl look to have a clear and transparent color.   * KOH tablets look smooth and their color is white.   * Shapes of KOH tablets are circled tablets.   * Solid KOH tablets look to have dissolved after some time.   * No specific smell recorded. |
Route 2 |     * During first reaction of turning solid KOH to aqueous KOH, the KOH tablets remain white-circled tablets when added to water.   * The new solution of aqueous KOH is noticed to have dissolved when added to HCl since no tablets appear after some time. |

Quantitative Raw Data:
Route 1:
Table 2: Mass and Temperature of Potassium Hydroxide in reaction 1:

Mass of Solid Potassium Hydroxide | 1.19g ± 0.01g |
The temperature of the acid before the reaction | 23.7℃ ± 0.1℃ |
Highest Temperature reached by the reaction mixture | 29.6℃ ± 0.1℃ |
Volume of HCl taken | 0.0242dm3 ± 0.0001dm3 |
Route 2: Table 2: Mass and Temperature of Potassium Hydroxide in reaction...