Exothermic Reaction
English
Activity:tivity: SetupSetup
Equipment
This activity uses the neutralization of hydrochloric acid and sodium hydroxide to study heat that is given off or absorbed by chemical reactions.
Theory
A chemical reaction causes a change in the properties of matter, and always gives off or absorbs heat. The sum of the heat of reaction when a chemical reaction takes place depends solely on the condition of the matter at the time of the reaction, and is totally independent of the reaction pathway and the number of steps between the initial state and the final state. This is called Hess’s law.
The following illustrates the chemical reaction when sodium chloride (aq) is generated from sodium hydroxide (s) and hydrochloric acid (aq).
NaOH(s) + aq = NaOH(aq) + 44.5kJNaOH(aq) + HCl(aq) = NaCl(aq) + H2O + 56.4kJNaOH(s) + HCl(aq) = NaCl(aq) + H2O + 100.9kJ1Reaction Path 1
2Reaction Path 2
3Energy
4Solvent (Water)
s: solid aq : aqua
Here, Reaction Path 1 includes the heat of dissolution when sodium hydroxide (s) is dissolved in distilled water, and the heat of neutralization of sodium hydroxide (aq) and hydrochloric acid (aq).
Reaction Path 2, on the other hand, consists of the heat of neutralization of sodium hydroxide (s) and hydrochloric acid (aq).
All of this means that the total heat is the same, regardless of whether or not the pathway includes a process for dissolving the sodium hydroxide (s), as in Reaction Path 1.
Stand | Auto Stirrer | Beaker (3) |
Hydrochloric Acid (Solution) | Sodium Hydroxide (Solid) | Distilled Water |
Temperature Measurement Setup
Setting Up
uMeasure the mass of the hydrochloric acid (aq) and distilled water to be used in the activity.
uMeasure the amount of sodium hydroxide (s) required so the number of its moles is equal to that of the hydrochloric acid (aq).
uFix the probe in place at a point between the center of the beaker and the wall of the beaker, in a location where it does not strike the stirrer’s magnet, at a depth so it is sufficiently immersed in the solution.
1Stand
2Auto Stirrer
3Beaker
4Temperature Probe (CH1)
5Solution
6
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