When we put barium hydroxide in the beaker of ammonium chloride and stir properly the temperature of the beaker increases or decreases?

In this demonstration or class experiment, students observe an endothermic reaction between solid hydrated barium hydroxide and solid ammonium chloride. The reaction produces a liquid that evolves into ammonia gas, with a dramatic drop in temperature to about –20 °C

Table of Contents Show

Health, safety and technical notes
Teaching notes
Endothermic reaction
Examples of an endothermic reaction

Although the experiment can be safely carried out as a class experiment (with GCSE or A-level candidates in mind), it lasts only about 5 minutes and may not be worth the extra time spent by students setting up and clearing away. Therefore it is recommended as being more suitable as a teacher demonstration. Students could be allowed to feel the outside of the very cold container.

Equipment

Apparatus

Eye protection (goggles)
Beaker, 100 cm3
Watch glass
Thermometer, reading to –30 °C (note 3)
Top-pan balance
Fume cupboard (optional)

Chemicals

Barium hydroxide-8-water (CORROSIVE), 32 g
Ammonium chloride (HARMFUL), 10 g
Concentrated hydrochloric acid (CORROSIVE)
Universal indicator (or litmus) paper, 1 strip

Health, safety and technical notes

Wear eye protection (goggles) throughout.
Work in a fume cupboard unless the room is well ventilated.
Consider using a thermocouple type thermometer which can be connected to a large display or computer monitor.
Barium hydroxide-8-water, Ba(OH)2.8H2O(s), (CORROSIVE) – see CLEAPSS Hazcard HC010B. Avoid lumps as far as possible when weighing out the required amount.
Ammonium chloride, NH4Cl(s), (HARMFUL) – see CLEAPSS Hazcard HC009a. Avoid lumps as far as possible when weighing out the required amount.
Concentrated hydrochloric acid, HCl(aq), (CORROSIVE) – see CLEAPSS Hazcard HC047a. Use a small stock bottle to provide fumes for the ammonia test.

Procedure

Stand the beaker on a watch glass containing a few drops of water, so that the base of the beaker is touching the water.
Note the room temperature.
Mix the two solids in the beaker and stir with the thermometer. The mixture becomes slushy as a liquid is formed, together with a white suspension.
The presence of ammonia can be detected by smell, and confirmed by blowing fumes from the hydrochloric acid bottle across the beaker’s mouth and by using moist indicator paper.
Observe the drop in temperature, which is confirmed by the fact that the beaker freezes to the watch glass.

Teaching notes

It helps to use a large thermometer display. The cold beaker can be passed around the class once the evolution of ammonia has stopped.

It is not possible to determine easily the exact barium compound or compounds produced in this reaction but the equation is usually represented as:

Ba(OH)2.8H2O(s) + 2NH4Cl(s) → 2NH3(g) + 10H2O(l) + BaCl2(s)

Ba(OH)2.8H2O(s) + 2NH4Cl(s) → 2NH3(g) + 8H2O(l) + BaCl2.2H2O(s)

A-level students could be asked to calculate the value of the enthalpy and entropy changes for the reaction, using standard enthalpy changes of formation and standard entropy values obtained from a data book or from the table below.

Compound	DHf⦵ / kJ mol-1	S⦵ / J mol-1 K-1
Ba(OH)2.8H2O(s)	-3345	427
NH4Cl(s)	-314	95
NH3(g)	-46	192
H2O(l)	-286	70
BaCl2(s)	-859	124
BaCl2.2H2O(s)	-1460	203

An enthalpy change of +164 kJ mol–1 is obtained if the product is assumed to be BaCl2(s), and +135 kJ mol–1 if it is assumed to be BaCl2.2H2O(s). Students should be able to predict qualitatively that the entropy change for the system has a positive value because a gas and a liquid are formed from two solids. From the values above they could also be asked to calculate the actual entropy change for the system and the surroundings, and hence ∆Stotal or ∆G for the reaction and confirm that the process is spontaneous. A value of ∆Ssystem of +591 J mol–1 K–1is obtained if the product is assumed to be BaCl2(s) and +530 J mol–1 K–1 if it is assumed to be BaCl2.2H2O(s).

Answer:

The reaction between Ammonium chloride and Barium hydroxide is an endothermic reaction.

Ba(OH)2 +2NH4Cl → BaCl2 + 2NH3 + 2H2O

Ammonium Chloride is slightly acidic and Barium Hydroxide very basic so will get an acid-base reaction.

This reaction is used to recover ammonia in the preparation of sodium carbonate from NaCl.

Endothermic reaction

Endothermic reactions are chemical reactions wherein the reactants absorb heat from the environment to produce products. These reactions cause a cooling effect by lowering the temperature of the surrounding area.

The system absorbs heat from the surroundings.
The entropy of the surrounding decreases (ΔS <0).
Enthalpy change (ΔH) is positive.

Examples of an endothermic reaction

Few examples of endothermic reactions are

Evaporation of liquid water, forming water vapour.
The baking of bread.

Check out the video below to know more about the types of organic reactions

Further Reading

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Introduction

Two dry solids --- barium hydroxide and ammonium nitrate --- are mixed to produce an endothermic reaction. The temperature of the mixture drops approximately 45oC and is cold enough to freeze the reaction beaker to water on a block of wood

Equations

Ba(OH)2.8H2O(s) + 2NH4NO3(s) → Ba(NO3)2(aq) + 2NH3(aq) + 10H2O(l)

To Conduct Demonstration

- Mix the two solids together in a 250mL beaker. Stir for a few seconds with a stirring rod. (Do not stir with the thermometer.) The mixture should become moist from the water released by the Ba(OH)2.8H2O. DO NOT ADD ANY WATER TO THE BEAKER.
- Place a drop or two of water on the wooden block. Place the container on top of the block of wood, covering the water.
- Place the thermometer in the beaker.
- The mixture will become extremely cold and freeze the reaction beaker to the damp block of wood. The entire block can be lifted up by lifting the beaker.
- This reaction releases NH3 gas. Students may be able to detect the odor if they are close enough.
- Read the final temperature from the thermometer.

Demo Time: 10 – 15 minutes

Safety and Disposal

Barium salts are toxic. Avoid inhaling ammonia vapors.

Dispose of waste in the barium waste carboy or the heavy metals waste carboy.

References

Shakhashiri, B.Z. Chemical Demonstrations: A Handbook for Teachers of Chemistry; 1983.

Acknowledgment

Margaret Asirvatham, Spring 1987.