Chemistry

PERCOBAAN REAKSI EKSOTERM DAN ENDOTERM

1. Tujuan

1. Mengamati terjadinya reaksi eksoterm dan reaksi endoterm
2. Mengamati ciri-ciri reaksi eksoterm dan reaksi endoterm
3. Mempelajari perubahan energi pada reaksi kimia

2. Dasar Teori

Reaksi eksoterm dan reaksi endoterm

1. Reaksi eksoterm

Reaksi eksoterm adalah reaksi yang menghasilkan kalor.

Kalor dilepas dari sistem ke lingkungan sehingga entalpi sistem berkurang dan perubahan entalpi berharga negatif.

∆H = Hp – Hr <>

2. Reaksi endoterm

Reaksi endoterm adalah reaksi kimia yang memerlukan kalor.

Kalor diserap dari lingkungan ke sistem sehingga entalpi dalam sistem bertambah dan perubahan entalpi berharga positif.

∆H = Hp – Hr > 0

1. Alat dan Bahan

1. Tabung reaksi
2. Rak tabung reaksi
3. Gabus tabung reaksi
4. Pipet
5. Penjepit tabung reaksi
6. Spatula
7. Alat pembakar
8. Korek api
9. Larutan asam klorida (HCl) 2 M
10. Magnesium (Mg)
11. Barium hidroksida oktahidrat (Ba(OH)₂ . 8H₂O)
12. Amonium Klorida (NH­₄Cl)
13. Serbuk Belerang (S)
14. Serbuk Besi (Fe)
15. Tembaga (II) Carbonat (CuCO₃)

1. Hasil Pengamatan

No	Kegiatan	Hasil Pengamatan
1.	Pencampuran HCL dan Pita Magnesium	- Terjadi reaksi kimia - Mengeluarkan banyak gelembung seperti mendidih. - Pita magnesium menjadi bersih / putih. - Pita magnesium melebur dan mulai habis. - Reaksi menimbulkan uap. - Menghasilkan panas.
2.	Pencampuran Ba(OH)2 . 8H2O dan NH4Cl. Pembauan gas.	- Wujud campuran setelah terjadi reaksi adalah aquos (larutan) - Suhu campuran adalah dingin - Menghasilkan bau gas menyengat (busuk) - Warna menjadi sedikit kebiru-biruan
3.	Pemanasan serbuk belerang (S) dan serbuk besi (Fe)	- Ketika dipanaskan, reaksi berjalan o Mengeluarkan gelembung seperti sata mendidih o Mengeluarkan pijaran api berwarna biru o Warna berubah menjadi hitam - Ketika pemanasan dihentikan o Pijaran masih bisa menyala selama beberapa detik kemudian berhenti.
4.	Pemanasan CuCO3 ketika pemanasan dihentikan	- Ketika dipanaskan, reaksi berjalan, CuCO3 berubah menjadi hitam. - Ketika pemanasan dihentikan, reaksi berhenti.

2. Pertanyaan

2) Jika reaksi dibiarkan beberapa jam, apa yang anda harapkan terjadi dengan suhu campuran pada (1) dan (2)?

3) Bagaimanakah jumlah entalpi zat-zat hasil reaksi (1), (2), (3), dan (4) jika diukur pada suhu dan tekanan yang sama?

4) Gambarlah diagram tingkat energi untuk keempat reaksi di atas!

5) Simpulkanlah pengertian reaksi eksoterm dan endoterm

3. Menjawab Pertanyaan

2) Jika hasil reaksi dibiarkan beberapa jam dan reaksi telah berakhir maka diharapkan suhu akan kembali ke keadaan normal.

(1) Reaksi disertai pelepasan atau pembebasan kalor, ketika reaksi selesai maka diharapkan suhu menurun menjadi normal.

(2) Reaksi disertai pengikatan kalor, ketika reaksi selesai diharapkan suhu naik menjadi normal.

1. Pembahasan

1) Pencampuran HCl dan pita Magnesium menghasilkan panas. Reaksi kimia yang menghasilkan panas adalah reaksi eksoterm. Reaksi eksoterm mempunyai Hr <>

2 HCl_(l) + Mg_(s) → MgCl_2(aq) + H_2(g) ∆H = -

2) Pencampuran Ba(OH)₂ . 8 H₂O dan NH₄Cl. Pembauan gas, menghasilkan suhu dingin dan bau gas. Reaksi ini termasuk reaksi endoterm. Reaksi endoterm mempunyai Hr > Hp sehingga ∆H berharga positif. Maka persamaan termokimianya adalah

Ba(OH)₂ . 8 H₂O_(s) + 2NH₄Cl_(s) → Ba(OH)_2(aq) + 2 NH₄OH_(aq) ∆H = +

2. Kesimpulan

1) Reaksi eksoterm adalah reaksi yang disertai pelepasan kalor ke lingkungan dan mempunyai harga perubahan entalpi negatif.

2) Reaksi endoterm adalah reaksi yang disertai perpindahan kalor dari lingkungan ke sistem dan mempunyai harga perubahan entalpi positif.

3) Reaksi (1) dan (3) termasuk reaksi eksoterm, sedangkan reaksi (2) dan (4) termasuk reaksi endoterm.

Chemistry Worksheet

How is the effect of the concentration to the chemical equilibrium?

A. Objective:

            To see the effect of the concentration change to the chemical equilibrium.

B.  Tools and Materials

            1. Reaction tube                                                              

            2. Pasteur pipette

3. Reaction tube rack                                                         

4. Chemical glass

5. Swirling stick                                                                

6. Aquades

            7. FeCl₃ solution 1M                                                    

            8. KSCN solution 1M

            9. Crystal Na₂HPO₄

 

C.  Steps

1. Pour 50 ml aquades to the chemical glass

2. By using Pasteur pipette, add 4 drops of FeCl₃ solution 1M and 4 drops of KSCN solution 1M into the chemical glass with aquades! Stir it until the color is homogeny.
3. Prepare 5 reaction tubes! Pour each of reaction tube with the same amount of solution from chemical glass. Give it with number I, II, III, IV, and V!
4. Reaction tube number I is used to compare the solution colors.
5. Add 1 drop of FeCl₃ solution 1M to the reaction tube number II!
6. Add 1 drop of KSCN solution 1M to the reaction tube number III!
7. Add crystal Na₂HPO₄ to the reaction tube number IV!
8. Add aquades to the reaction tube number V, save it with reaction tube number I for the next experiment.
9. Compare the solution colors at reaction tube number II, III, and IV to the solution colors at reaction tube number I! Write down your observation!

D. Observation Result

      The chemical equation: Fecl_3(aq) + 3 KSCN_(aq)  FeSCN²⁺_(aq) + 3 KCl_(aq)

No. of the Reaction tube	Treatment	The colors of observation result
I	-	Orange
II	+ 1 drop of FeCl3 1M	Sorrel
III	+ 1 drop of KSCN 1 M	Condensed red
IV	+ Na2HPO4 crystal	Transparent

E.  Question

1. What is the solution color at reaction tube number I?
2. How is the solution color at tube II compared with the solution color of tube I?
3. How is the solution color at tube III compared with the solution color of tube I?
4. How is the solution color at tube IV compared with the solution color at tube I?
5. What is the purpose by adding FeCl₃ at reaction tube number II? Explain!
6. What is the purpose by adding KSCN at reaction tube number III? Explain!
7. What is the purpose by adding crystal Na₂HPO₄ at reaction tube number IV? Explain!
8. What is the conclusion of the observation?
9. How is the equilibrium chemical reaction at this observation?

Answers

1. The solution color at the reaction tube number 1 is orange.
2. The solution color at the reaction tube number 2 is sorrel or become darker.
3. The solution color at the reaction tube number 3 is condensed red or become darker than the solution color at the reaction tube number 2.
4. The solution color at the reaction tube number 4 is transparent or become clear.
5. To see the shift of the chemical equilibrium if one of the concentration of the reactant is bigger.  It shows by the darker color caused the chemical equilibrium shift to the product.
6. To see the shift of the chemical equilibrium if one of the concentration of the reactant is bigger.  It shows by the darker color caused the chemical equilibrium shift to the product.
7. To see the shift of the chemical equilibrium if another substance is added.  It shows by transparent color caused by Na₂HPO₄ bonds the ion Fe³⁺.
8. The concentration change can affect the shift of the chemical equilibrium.  If the concentration of the substances is bigger, the chemical equilibrium will shift away from the substances, and the color of the products will become darker.  In this experiment, the solution color becomes darker when the concentration of the reactant is bigger.  Oppositely, if the concentration of the substances is lower, the chemical equilibrium will shift away to the substances, and the color of the products will become clearer.  In this experiment, the solution color becomes transparent caused by the reduction of the product.
9. The chemical equilibrium shifts by following the Le Chatelier principle.