Welcome to this spoken tutorial Heat of Reaction using Vlabs.
In this tutorial, we will learn to, Determine heat change for the neutralisation of Sodium hydroxide (NaOH) and Hydrochloric acid(HCl).
Calculate heat of reaction for three different reactions.
The three reactions are shown here.
To follow this tutorial you should be familiar with, ChemCollective Vlabs interface.
If not, for relevant tutorials please visit our website.
Here, I am using Mac OS 10.10.5
ChemCollective Vlabs version 2.1.0 Java version 8.
I have opened a Virtual Chemistry lab application window.
Click on File and select Load homework option.
Default Lab setup dialog box opens.
In the box, select Thermochemistry.
Double click on Heats of the reaction- Hess’s Law option.
Click on Problem Description in Stockroom Explorer.
The Problem Descriptionhere states that, we have to determine and compare heat of reaction for 3 different reactions.
Scroll down the page and read, Procedure, Processing the data, Discussion and Conclusion
This experiment is an illustration of Hess's law.
Which states that , total heat change during the complete course of a reaction is same, whether the reaction is made in one step or in several steps.
Heat of reaction is also known as Standard enthalpy change.
delta rH = delta r H 1 + delta r H 2 + delta r H 3 ,etc.
Sum of Heats of reactions for, Reaction 1 and Reaction 3 must be equal to heat of reaction for Reaction 2.
Let us go back to Workbench. We will begin the first reaction.
Let us select the required chemicals and apparatus for the reaction.
From the Chemical Stockroom, Double-click on Distilled water.
Click on Solids cabinet and double-click on Sodium hydroxide. Close the cabinet.
From the glassware menu, we will select a 50 mL Graduated Cylinder and a Foam Cup.
From the instrument menu, select Weighing Boat and a Scale.
Transfer 50 mL of Distilled water to the Graduated Cylinder.
In the Transfer amount input bar, type 50 and click on Pour.
Weigh 1 gram of Sodium hydroxide using Weighing Boat.
Place the Weighing Boat on the Scale, click on TARE.
Drag the Sodium hydroxide bottle over the weighing boat.
Type 1 in the Transfer amount input bar and click on Pour .
Transfer Sodium hydroxide from Weighing Boat to Foam Cup. Click on Pour.
Click on Foam Cup. In the Solution info panel, Click on Solid radio button and observe the weight in grams column.
Click on the Graduated Cylinder and record its temperature. Thermometer shows the temperature as 25 degrees Celsius.
Drag the Graduated Cylinder over to the Foam Cup. Type 50 in the Transfer Amount input bar and click on Pour.
Click on Foam Cup. Record the highest temperature on the thermometer.
Thermometer shows 30.29 degrees Celsius.
Observe the grams column, it shows zero. This is because all the Sodium hydroxide has now dissolved in water.
Lets see how to calculate heat of the reaction.
Heat of reaction (q) is calculated using the formula. q = m * s * ∆T wherein 'm' is mass of the reactants
's' is the specific heat of the product and '∆T' is the change in temperature in the reaction.
Heat energy calculation for this reaction is given here.
Calculation of Molar Heat energy (delta H) in Kilo Joules per mol is given here.
delta H for reaction 1 Sodium hydroxide is -45.32 Kilo Joules per mol
Lets go back to workbench. Let us delete the used Graduated Cylinder and Foam Cup.
We will now move on to demonstrate second exothermic reaction.
From Glassware menu, Take a new 50 mL Graduated Cylinder and a Foam Cup.
From the Chemical Stockroom, select Strong-acids cabinet. Double click to get 0.5 M Hydrochloric acid.
Close the Cabinet.
Transfer 50 mL of Hydrochloric acid into the Graduated Cylinder.
Weigh 1 gram of Sodium hydroxide using Weighing Boat.
Transfer Sodium hydroxide from Weighing Boat to Foam Cup.
Click on the Graduated Cylinder, record its temperature.
Pour the contents of the Graduated Cylinder into the Foam Cup.
Click on the Foam Cup. Record the highest temperature on the thermometer.
Thermometer shows 36.96 degree Celcius.
Calculation of Molar Heat energy (delta H) in Kilo Joules per mol is given here.
delta H for Reaction 2 is -102.47 Kilo Joules per mol
Delete the used apparatus and chemicals from the Workbench.
From Glassware menu take a new 25 mL Graduated Cylinder and a Foam Cup
We need two Graduated Cylinders. Use Duplicate option in the context menu to make the copies.
Drag both the cylinders to a convenient place on the Workbench.
Label the cylinders as A and B.
From the Chemical Stockroom click on Strong-acids cabinet. Double click on 1.0 M Hydrochloric acid.
Close the cabinet. From the Strong-bases cabinet, double click on 1.0 M Sodium hydroxide.
Close the cabinet.
Transfer 25 mL of Hydrochloric acid(HCl) into graduated cylinder A.
Pour the Hydrochloric acid(HCl) from graduated cylinder to Foam Cup.
Note the temperature on the thermometer.
Measure 25 mL of Sodium hydroxide in Graduated Cylinder B.
Pour the measured Sodium hydroxide into the Foam Cup.
Click on Foam Cup. Allow the reaction to take place for a few seconds.
Record the highest temperature. Thermometer shows 31.67 degree Celcius.
Calculation of Molar Heat energy for reaction three is given here. delta H for reaction 3( Rx3) is -56.03 Kilo Joules per mol
Now, Let us now analyze the results. The value of Sum of heats of reactions for Reaction 1 and Reaction 3 is -101.35 Kilo Joules per mol
The value of heat of reaction for Reaction 2 is -102.47 Kilo Joules per mol. Therefore this experiment illustrates Hess's law.
Let us summarize.
In this tutorial we have, Determined heat change for neutralization of Sodium hydroxide and Hydrochloric acid.
Calculated heat of reaction for 3 different reactions.
For the assignment, Explain why the reactions are exothermic.
Repeat Reaction 1 using 4 grams of Sodium hydroxide and calculate the heat of reaction.
Compare its value with the reaction in which 1 gram of Sodium hydroxide was used.
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This tutorial is contributed by Snehalatha kaliappan and Madhuri Ganapathi from IIT Bombay. Thank you for joining.