Difference between revisions of "ChemCollective-Virtual-Labs/C3/Heat-of-Reaction/English"

Title Slide

Learning Objectives

Determine heat change for the neutralisation of Sodium hydroxide (NaOH) and Hydrochloric acid(HCl).

Calculate heat of reaction for three different reactions.

Reactions

Rx1: NaOH(s) +H₂O(l) ->

Na⁺(aq) + OH^-(aq)

Rx2: NaOH (s) + HCl (aq) ->

Na⁺(aq) + Cl^-(aq)+H₂O

Rx3: NaOH (aq) + HCl (aq) ->

Na⁺(aq) + Cl^-(aq) +H₂O(l)

Pre-requisites

www.spoken-tutorial.org

ChemCollective Vlabs interface.

If not, for relevant tutorials please visit our website.

System Requirement

Mac OS 10.10.5

ChemCollective Vlabs version 2.1.0

Java version 8.

double-click on vlabs.exe file.

Default Lab setup dialog box opens.

Thermochemistry >> Heat of the reaction

Default Lab setup dialog box opens.

In the box, select Thermochemistry.

Double click on Heats of the reaction- Hess’s Law option.

Scroll down the page and highlight the words Procedure, Processing Data, discussion and Conclusion.

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

Hess’s Law

∆ rH = ∆ r H 1 + ∆ r H 2 + ∆ r H 3 ….

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.

Hess’s law

ΔH1 + ΔH3 = ΔH2

Rx1 + Rx3= Rx2

Rx1: NaOH(s) +H₂O(l) ->

Na⁺(aq) + OH^-(aq)

Rx3: NaOH(aq) + HCl(aq) ->

Na⁺(aq) + Cl^-(aq) +H₂O(l)

Rx2: NaOH (s) + HCl (aq) ->

Na⁺(aq) + Cl^-(aq)+H₂O

Rx1 and Rx3 must be equal to heat of reaction for Rx2.

Rx=reaction

We will begin the first reaction.

Let us select the required chemicals and apparatus for the reaction.

Double-click on Distilled water .

Go to Solids

Double click on Sodium hydroxide icons.

Double-click on Distilled water.

Click on Solids cabinet and double-click on Sodium hydroxide.

Close the cabinet.

In the Transfer amount input bar, Type 50. Click on Pour.

Keep the distilled water aside.

In the Transfer amount input bar, type 50 and click on Pour.

Click on TARE.

Place the Weighing Boat on the Scale, click on TARE.

Type 1 in the Transfer amount input bar.

Click on Pour.

Drag the Weighing Boat containing Sodium hydroxide bottle over Foam Cup.

Type 1 in the transfer amount input bar.

Click on Pour.

Type 1 in Transfer amount input bar and click on Pour .

Transfer Sodium hydroxide from Weighing Boat to Foam Cup.

Click on Pour.

Click on Solid radio button in the Solutions info panel, to see the weight in grams column.

In the Solution info panel,

Click on Solid radio button and observe the weight in grams column.

Drag the Graduated Cylinder to the Foam Cup.

Type 50 in the Transfer bar.

Click on Pour.

T1 = 25 ^o C.

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.

Record the highest temperature on the thermometer.

Thermometer shows 30.29 degrees Celsius.

This is because all the Sodium hydroxide has now dissolved in water.

Heat of Reaction (q)

Formula

q = m * s *∆T

m = mass of the reactants

s = specific heat of the product

∆T = change in temperature in the reaction.

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.

Calculation of heat of reaction Rx1

q = m * s * ∆T

m = 50 ml water + 1 g NaOH

s = 4.2 KJ/g

∆T = (T1- T2) = (25-30.29) = -5.29

q = (50+1) * 4.2 * (-5.29)

q= -1133.12/1000= -1.133 KJ.

Calculation of heat of reaction Rx1

ΔH = q/moles of NaOH

Number of moles of NaOH is =1/40 = 0.025.

ΔH1 =-.133/0.025 = -45.32 KJ mol^-1

ΔH1= -45.32 KJ mol^-1

delta H for reaction 1(Rx1) Sodium hydroxide is -45.32 KJ mol^-1

Press delete.

let us delete the used Graduated Cylinder and Foam Cup.

Double-click on 50 mL Graduated Cylinder and Foam Cup.

From Glassware menu,

Take a new 50 mL Graduated Cylinder and a Foam Cup.

Double-click on 0.5 M Hydrochloric acid from the Strong-acids cabinet.

Double click to get 0.5 M Hydrochloric acid.

Close the Cabinet.

Type 50 in the Transfer bar.

Click on Pour.

Click on TARE.

Drag Sodium hydroxide bottle over to Weighing Boat.

Type 1 in the Transfer amount input bar.

Click on Pour.

Transfer Sodium hydroxide from Weighing Boat to Foam Cup.

Highlight the temperature.

T1 = 25 ^o C

Drag the Graduated Cylinder over Foam Cup.

Type 50 in the Transfer bar.

Click on Pour.

Pour the contents of the Graduated Cylinder into the Foam Cup.

Highlight the temperature.

T2 = 36.96 ^o C

Record the highest temperature on the thermometer.

Thermometer shows 36.96 ^o C.

Calculation of heat of reaction for Rx2

q = m * s * ∆T.

∆T = (T1- T2) = (25 - 36.96) = -11.96.

q = (50+1) * 4.2 * -11.96

q = -2561.83 Joules

q = -2561.83 /1000=-2.561 KJ

ΔH2 = -2.561/0.025 = -102.47 KJ mol^-1

delta H for reaction 2(Rx2) is -102.47 KJ mol^-1

Double-click on 25 mL Graduated Cylinder and a Foam Cup.

Right click on 25mL Graduated Cylinder.

Select the Duplicate option.

We need two Graduated Cylinders.

Use Duplicate option in the context menu to make two copies.

Use context menu to rename the cylinder as A and B .

Double-click on Strong-acids cabinet.

Double-click on 1.0 M HCl.

Double-click on Strong-bases cabinet.

Double-click on 1.0 M NaOH.

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.

Type 25 in the Transfer bar.

Click on Pour.

Click on the Graduated Cylinder.

Drag the Graduated Cylinder to the Foam Cup.

Type 25 in the Transfer bar.

Click on Pour.

Click on the Graduated Cylinder.

Highlight the temperature.

T1= 25^o C

Pour the Hydrochloric acid(HCl) from graduated cylinder to Foam Cup.

Note the temperature on the thermometer.

Type 25 in the transfer bar.

Click on Pour.

Drag the Graduated Cylinder to the Foam Cup.

Type 25 in the Transfer bar.

Click on Pour.

Highlight the temperature

T2 = 31.67 ^o C

Allow the reaction to take place for a few seconds.

Record the highest temperature.

Thermometer shows 31.67 ^o C.

Calculation of heat of reaction for Rx3

q = m * s * ∆T

∆T = (T1- T2) = (25 – 31.67) = -6.67

q =(25+25) * 4.2 * (-6.67)

q= -1400.7 Joules

q = -1400.7 /1000 = -1.400 KJ

ΔH3 =-1.400/0.025 = -56.03 KJ mol^-1

delta H for reaction 3( Rx3) is -56.03 KJ mol^-1

Analysis of Results

This experiment is an example for Hess's law.

ΔH1 + ΔH3 = ΔH2

ΔH1 + ΔH3= (-45.32 KJ mol^-1 + -56.03 KJ mol^-1 ) = -101.35 KJ mol^-1

ΔH2 = -102.47 KJ mol^-1

The value of Sum of heats of reactions for Rx1 and Rx3 is -101.35 KJ mol^-1

Rx=reaction

The value of heat of reaction for Rx2 is -102.47 KJ mol^-1

Therefore this experiment illustrates Hess's law.

Summary

Determined heat change for neutralization of Sodium hydroxide

and Hydrochloric acid.

Calculated heat of reaction for 3 different reactions.

Assignment

q = m * s * ∆T

q = (50+4) x 4.2 x (-21.18) = -4803.62 Joules

ΔH = -4803.62 /1000 = -4.803

ΔH = -4.803/0.1 = -48.03 KJ mol^-1

Explain why the reactions are exothermic.

Repeat Rx1 using 4 g of Sodium hydroxide and

calculate the heat of reaction.

Compare its value with the reaction in which 1 g of Sodium hydroxide was used.

About Spoken Tutorial project

Please download and watch it.

Spoken Tutorial workshops

conducts workshops using spoken tutorials and

gives certificates on passing online tests.

For more details, please write to us.

Forum for specific questions

Do you have questions in THIS Spoken Tutorial?

Please visit this site

Choose the minute and second where you have the question

Explain your question briefly

Someone from our team will answer them

Acknowledgement

More information on this mission is available at this link.

Thank you for joining.