Calculate the molar enthalpy change for two reactions and use Hess’s law to determine the enthalpy change for the thermal decomposition of potassium hydrogencarbonate (KHCO3) Reagents (these quantities allow two repeats of each experiment. Some additional quantity may be needed for additional repeats) 2 mol dm–3 HCl (at least 120 cm3 per pair/group) Solid K2CO3 (approx. 6 g per pair/group). This should be anhydrous and dried before use. Solid KHCO3 (approx. 7 g per student) Materials (per pair/group) Thermometer (that reads up to 50 °C or more) Polystyrene cups with lid/cardboard cover (students could punch the holes themselves) Burette, clamp and stand, stirring rod Materials (general): analytical balances, spatulas, weighing boats Method NOTE: repeat the experiment at least twice for each chemical (K2CO3 and KHCO3). In between experiments, empty the solution from the calorimeter down the sink, wash and dry the calorimeter. Place approximately 3 g of solid K2CO3 in a weighing boat. Record the exact weight Use a burette to dispense 30 cm3 of 2 mol dm–3 HCl into the nested polystyrene cups. Measure the temperature of the acid. Continue measuring the temperature whilst adding the K2CO3 to the acid and stirring. Record the highest temperature reached. Reweigh the empty weighing boat. Repeat steps 1 to 5, but this time using approximately 3.5 g of KHCO3 instead of K2CO3. This time record the lowest temperature reached. Write the chemical equations that describe the reactions which take place on step 1-5 when using K2CO3(s) and KHCO3(s). Calculate the enthalpy for both reactions. Compare the enthalpy results obtained with the published literature data for each reaction. Decide if you need more repeats of one or both experiments. Write the chemical equation that describe the decomposition of KHCO3(s). Calculate the enthalpy for the reaction and compare with literature values.

Calculate the molar enthalpy change for two reactions and use Hess’s law to determine the enthalpy change for the thermal decomposition of potassium hydrogencarbonate (KHCO3) Reagents (these quantities allow two repeats of each experiment. Some additional quantity may be needed for additional repeats) 2 mol dm–3 HCl (at least 120 cm3 per pair/group) Solid K2CO3 (approx. 6 g per pair/group). This should be anhydrous and dried before use. Solid KHCO3 (approx. 7 g per student) Materials (per pair/group) Thermometer (that reads up to 50 °C or more) Polystyrene cups with lid/cardboard cover (students could punch the holes themselves) Burette, clamp and stand, stirring rod Materials (general): analytical balances, spatulas, weighing boats Method NOTE: repeat the experiment at least twice for each chemical (K2CO3 and KHCO3). In between experiments, empty the solution from the calorimeter down the sink, wash and dry the calorimeter. Place approximately 3 g of solid K2CO3 in a weighing boat. Record the exact weight Use a burette to dispense 30 cm3 of 2 mol dm–3 HCl into the nested polystyrene cups. Measure the temperature of the acid. Continue measuring the temperature whilst adding the K2CO3 to the acid and stirring. Record the highest temperature reached. Reweigh the empty weighing boat. Repeat steps 1 to 5, but this time using approximately 3.5 g of KHCO3 instead of K2CO3. This time record the lowest temperature reached. Write the chemical equations that describe the reactions which take place on step 1-5 when using K2CO3(s) and KHCO3(s). Calculate the enthalpy for both reactions. Compare the enthalpy results obtained with the published literature data for each reaction. Decide if you need more repeats of one or both experiments. Write the chemical equation that describe the decomposition of KHCO3(s). Calculate the enthalpy for the reaction and compare with literature values.

Chemistry

10th Edition

ISBN:9781305957404

Author:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste

Publisher:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste

Chapter1: Chemical Foundations

Section: Chapter Questions

Problem 1RQ: Define and explain the differences between the following terms. a. law and theory b. theory and...

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Calculate the molar enthalpy change for two reactions and use Hess’s law to determine the enthalpy change for the thermal decomposition of potassium hydrogencarbonate (KHCO₃)

Reagents (these quantities allow two repeats of each experiment. Some additional quantity may be needed for additional repeats)

2 mol dm^–3 HCl (at least 120 cm³ per pair/group)

Solid K₂CO₃ (approx. 6 g per pair/group). This should be anhydrous and dried before use.

Solid KHCO₃ (approx. 7 g per student)

Materials (per pair/group)

Thermometer (that reads up to 50 °C or more)
Polystyrene cups with lid/cardboard cover (students could punch the holes themselves)
Burette, clamp and stand, stirring rod
Materials (general): analytical balances, spatulas, weighing boats

Method

NOTE: repeat the experiment at least twice for each chemical (K₂CO₃ and KHCO₃). In between experiments, empty the solution from the calorimeter down the sink, wash and dry the calorimeter.

Place approximately 3 g of solid K₂CO₃ in a weighing boat. Record the exact weight
Use a burette to dispense 30 cm³ of 2 mol dm^–3 HCl into the nested polystyrene cups.
Measure the temperature of the acid.
Continue measuring the temperature whilst adding the K₂CO₃to the acid and stirring. Record the highest temperature reached.
Reweigh the empty weighing boat.
Repeat steps 1 to 5, but this time using approximately 3.5 g of KHCO₃ instead of K₂CO₃. This time record the lowest temperature reached.
Write the chemical equations that describe the reactions which take place on step 1-5 when using K₂CO₃(s) and KHCO₃(s). Calculate the enthalpy for both reactions. Compare the enthalpy results obtained with the published literature data for each reaction. Decide if you need more repeats of one or both experiments.
Write the chemical equation that describe the decomposition of KHCO₃(s). Calculate the enthalpy for the reaction and compare with literature values.

Mass of weighing boat with the
chemical (g)
Mass of empty weighing boat
(at the end of the trial)
Mass of chemical used (g)
Start temperature (°C)
Highest (or lowest)
temperature (°C)
Temperature change
Potassium carbonate Potassium hydrogencarbonate
5.35
2.25
3.1
23.2
28.4
5.2
6.23
3.01
3.22
23.1
19.2
-3.9

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