HUKUM HESS, ENTALPI PEMBENTUKAN DAN ENERGI IKATAN

Summary

This educational video script discusses the application of Hess's Law in thermodynamics, focusing on calculating reaction enthalpy changes. It presents examples involving the reaction of NH3 with HCl to form NH4Cl, demonstrating how to determine the enthalpy change using initial and final states. The script further illustrates how to manipulate chemical equations to align with known enthalpy values and calculate the enthalpy change for reactions such as S + O2 to SO2 and SO3. It also covers the calculation of reaction enthalpy using standard enthalpy formation data for C3H8 combustion and the use of bond energy data to determine the enthalpy change for the combustion of CH4.

Takeaways

• 🔍 The script discusses the application of Hess's Law in calculating the enthalpy change of chemical reactions.
• 📚 It explains that the enthalpy change of a reaction depends only on the initial and final states, not the path taken.
• 🧪 The script provides an example of calculating the enthalpy change for the reaction between NH3 and HCl to form NH4Cl.
• 📐 It demonstrates how to adjust the direction of reactions and coefficients to match the given thermochemical equations.
• 🔢 The calculation involves summing the enthalpy changes of the reactants and products, taking into account their stoichiometric coefficients.
• 🌡 The script also covers the calculation of enthalpy change using standard enthalpies of formation for the combustion of C3H8.
• ⚖️ It highlights that the enthalpy of formation for diatomic gas molecules like O2, H2, and N2 is zero, simplifying calculations.
• 🔥 Another example provided involves the reaction of CH4 with O2 to form CO2 and H2O, emphasizing the importance of identifying the types of bonds in the reactants and products.
• 📈 The script explains that the enthalpy change of a reaction can be found by subtracting the energy of bond formation from the energy of bond breaking.
• 📝 It concludes with a detailed calculation for the enthalpy change of the combustion reaction of CH4, incorporating bond energies and stoichiometric coefficients.

Q & A

What is the first example problem discussed in the script?

The first example problem discusses the calculation of the enthalpy change for the reaction NH3 + HCl to form NH4Cl.

What is the significance of the term 'Delta H' in the context of the script?

In the script, 'Delta H' refers to the change in enthalpy, which is a measure of the heat absorbed or released in a chemical reaction.

How is the enthalpy change calculated for the reaction NH3 + HCl?

The enthalpy change for the reaction NH3 + HCl is calculated by considering the standard enthalpies of formation of the reactants and products, and it is found to be -176 kJ.

What is the second example problem in the script about?

The second example problem involves determining the enthalpy change for the reaction of sulfur and oxygen to form sulfur trioxide.

How does the script explain the application of Hess's Law?

The script explains Hess's Law by demonstrating how to calculate the enthalpy change of a reaction using the standard enthalpies of formation of reactants and products.

What is the role of stoichiometry in calculating the enthalpy change of a reaction?

Stoichiometry is crucial in calculating the enthalpy change as it determines the coefficients of reactants and products, which are used to calculate the total enthalpy change.

What is the significance of the term 'exothermic' in the script?

The term 'exothermic' is used in the script to describe a reaction that releases heat, such as the reaction NH3 + HCl forming NH4Cl.

How does the script handle the calculation when the reaction direction is reversed?

When the reaction direction is reversed, the script instructs to reverse the sign of the enthalpy change to maintain the correct calculation.

What is the third example problem presented in the script?

The third example problem is about calculating the enthalpy change for the combustion of propane (C3H8) using standard enthalpies of formation.

What is the purpose of identifying the type of bonds in the molecules involved in a reaction?

Identifying the type of bonds in the molecules is necessary to calculate the energy changes associated with bond breaking and formation, which are used to determine the enthalpy change of the reaction.

How does the script use bond energies to calculate the enthalpy change of a reaction?

The script uses bond energies by summing the energy required to break the bonds in the reactants and subtracting the energy released in forming the bonds in the products to find the enthalpy change.

Outlines

00:00

🔍 Application of Hess's Law in Chemical Reactions

This paragraph discusses the application of Hess's Law in calculating the enthalpy change of chemical reactions. It explains how the enthalpy change depends on the initial and final states of the reactants and products. The example provided involves the reaction of NH3 with HCl to form NH4Cl, and the calculation of the enthalpy change is demonstrated using the standard enthalpies of formation. The process involves adjusting the coefficients of the reactions to match the desired reaction and then summing the enthalpy changes of the individual steps to find the overall enthalpy change for the reaction. The result shows that the reaction is exothermic, releasing 176 kJ of heat.

05:05

🔬 Calculation of Reaction Enthalpy Using Standard Formation Enthalpies

The second paragraph focuses on determining the enthalpy change for a reaction using standard formation enthalpies. The example given is the combustion of propane (C3H8) with oxygen to form carbon dioxide and water. The process involves identifying the reactants and products and then using the standard formation enthalpies to calculate the enthalpy change of the reaction. The calculation takes into account the coefficients of the molecules in the balanced chemical equation and the fact that diatomic molecules like O2 have zero formation enthalpy. The final result is an enthalpy change of -2222 kJ for the reaction, indicating that it is exothermic.

10:06

🧪 Enthalpy Change Calculation with Bond Energy Data

The third paragraph delves into the calculation of enthalpy change using bond energy data, which is crucial for understanding the energy changes associated with breaking and forming chemical bonds. The example provided is the combustion of methane (CH4) with oxygen to produce carbon dioxide and water. The process requires identifying the types of bonds present in the reactants and products and then calculating the enthalpy change by summing the energy required to break the bonds in the reactants and subtracting the energy released in forming the bonds in the products. The calculation includes the bond energies of single and double bonds and the coefficients from the balanced chemical equation. The result is an enthalpy change of -808 kJ for the reaction, confirming it as an exothermic process.

Keywords

💡Enthalpy Change

Enthalpy change, often symbolized as ΔH, is a measure of the heat absorbed or released in a chemical reaction at constant pressure. It is a key concept in thermodynamics and is central to the video's theme of discussing chemical reactions. In the script, the calculation of enthalpy change for reactions such as NH3 + HCl producing NH4Cl is used to illustrate the concept, showing how it can be determined from standard enthalpy of formation values.

💡Hess's Law

Hess's Law states that the total enthalpy change for a reaction is the same, whether it occurs in one step or several steps. This principle is fundamental in the video as it is used to calculate the enthalpy change for reactions that are not directly measurable. The script provides examples of how to apply Hess's Law to determine the enthalpy change for complex reactions by combining data from simpler reactions.

💡Standard Enthalpy of Formation

The standard enthalpy of formation is the change in enthalpy during the formation of 1 mole of a compound from its elements, with all substances in their standard states at 298 K and 1 atm. This concept is integral to the video's discussion on calculating enthalpy changes for reactions. The script uses this term to explain how to calculate the enthalpy change for reactions by using the standard enthalpy of formation values of the products and reactants.

💡Exothermic Reaction

An exothermic reaction is a chemical reaction that releases energy in the form of heat. This is a key concept in the video, as it is used to describe the nature of certain reactions, such as the reaction between NH3 and HCl. The script mentions that the reaction has a negative enthalpy change, indicating that it is exothermic and releases 176 kJ of heat.

💡Endothermic Reaction

Conversely, an endothermic reaction absorbs energy from its surroundings. While not explicitly detailed in the script, the concept is implied when discussing reactions with positive enthalpy changes, suggesting that energy is absorbed.

💡Thermochemistry

Thermochemistry is the study of the heat and energy changes during chemical reactions. It is the overarching theme of the video, with the script focusing on how to calculate and understand these energy changes through various examples and principles like Hess's Law.

💡Enthalpy of Combustion

Enthalpy of combustion refers to the enthalpy change when one mole of a substance is burned in excess oxygen. This concept is related to the video's theme as it is a type of reaction where enthalpy changes are often measured. The script does not directly mention combustion, but understanding enthalpy changes in reactions is crucial for comprehending combustion processes.

💡Bond Energy

Bond energy is the energy required to break a particular chemical bond. It is a key concept in the video when discussing how to calculate the enthalpy change for reactions based on bond energies. The script uses bond energy values to calculate the enthalpy change for reactions, such as the combustion of methane (CH4).

💡Reversible Reaction

A reversible reaction is one in which the products can react to form the original reactants under the same conditions. This concept is important in the video's discussion of reaction mechanisms and equilibrium. While not explicitly mentioned in the script, understanding enthalpy changes in reactions is essential for analyzing reversible processes.

💡Calorimetry

Calorimetry is the technique used to measure the heat of physical or chemical processes. It is related to the video's theme as it is a practical application of enthalpy changes. The script does not directly discuss calorimetry, but the calculations and principles explained are fundamental to understanding and performing calorimetric measurements.

Highlights

Introduction to the first law of Hess, explaining the concept of enthalpy change in chemical reactions.

Discussion on calculating the enthalpy change for the reaction NH3 + HCl to form NH4Cl.

Explanation of how the initial and final states of a reaction determine the enthalpy change.

Misunderstanding corrected regarding the direction of the reaction for the calculation of enthalpy change.

Final calculation of the enthalpy change for the NH3 + HCl reaction, resulting in an exothermic reaction releasing 176 kJ of heat.

Transition to the second example problem involving the reaction of S and O2 to form SO3.

Application of Hess's law to determine the enthalpy change for the reaction of S and O2 to form SO2.

Correction of the stoichiometry and direction of the reaction to accurately calculate the enthalpy change.

Final calculation of the enthalpy change for the reaction of S and O2 to form SO2, resulting in a value of -494.3 kJ.

Introduction to the third example problem involving the combustion of C3H8 to form CO2 and H2O.

Explanation of how to use standard enthalpy of formation data to calculate the enthalpy change for a reaction.

Calculation of the enthalpy change for the combustion of C3H8, considering the stoichiometry of reactants and products.

Final calculation of the enthalpy change for the combustion of C3H8, yielding a value of -2222 kJ.

Introduction to the fourth example problem involving the reaction of CH4 with O2 to form CO2 and H2O using bond energy data.

Explanation of the process to calculate the enthalpy change using bond energy, focusing on breaking and forming bonds.

Final calculation of the enthalpy change for the reaction of CH4 with O2, resulting in a value of -808 kJ.

Emphasis on understanding the molecular structure and bond types involved in the reaction for accurate enthalpy change calculations.

Transcripts

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hai hai

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yo yo

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Hi Ho

hai hai

Oh

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ya Baiklah kita akan membahas contoh

soal hukum Hess yang pertama kalian

tidak kalian lihat di sini ini adalah Eh

ada siklus dari reaksi Ya gimana di sini

kalian diminta dari reaksi siklus ini

diminta berhitunglah nilai perubahan

entalpi reaksi dari reaksi NH3 + HCl

menghasilkan

nh4cl ya Nah kita ketahui bahwa

eh NH3 + HCl ini merupakan posisi awal

keadaan awal sementara nh4cl ini adalah

kondisi atau posisi akhirnya nah Berarti

menutup Omesh bahwa perubahan entalpi

reaksi hanya tergantung dari keadaan

awal dan akhir berarti yang lain

reaksinya harus menyesuaikan aku marah

nih ya Nah kita ketahui bahwa perubahan

entalpi Delta H2 ini ya dia tidak sesuai

arahnya berakhir harus dibalik reaksinya

ternyata H2 sementara untuk Delta H3

arah reaksinya sudah benar tetapi tidak

perlu di balik lagi sehingga untuk

penyelesaiannya ya untuk penyelesaiannya

tidak kita tulis aja ya tahap data hari

Aksi entalpi ini

= Min karena dibalik data H2 menjadi

ingin Delta H2 + Delta H3

kita masukkan nilainya delta H = min

Delta H2 + delta H 3 = min nilai dari

Delta H2 dalam in 138 Min kali min

138 plus-minus 314 kilojoule jadi

138 dikurang 314 Sirojul hasilnya in 176

dirojok berarti delta H reaksi atau

perubahan entalpi reaksi reaksi NH3 +

HCl menghasilkan nh4cl mempunyai nilai

sebesar mint 176 lucu bersifat eksoterm

melepaskan kalor sebesar 176 q&c

baiklah kita lihat contoh soal yang

kedua Diketahui data sebagai berikut

SS3 berdua O2 menghasilkan so3 dimana

Delta hanya mint 395 2 kilo joule 2 so2

+ O2 menghasilkan 2 so3 Delta hanya =

positif

198.com 2 kilo joule pertanyaannya

tentukanlah delta H reaksi

jadi yang perlu kalian pahami

pada hukum Hess ini adalah

pada call center posisi awal atau reaksi

awal dari aksi akhirnya ia menjadi acuan

ya

cce jadi yang menjadi acuan adalah

reaksi

S + O2 menghasilkan so2

yang pergi ini memperhatikan

S + O2 harus ada di posisi sebelah kiri

sesuaikan S + O2 sudah dari sebelah kiri

atau belok ternyata sudah berarti tidak

perlu dibalik ya Sebentar ya yang kedua

ya

so-2f sebelah kanan sementara reaksi

yang kedua diketahui so2 sebelah kiri ya

berarti harus dibalik ya dibalik dan

koefisien so2 adalah satu sementara

didata adalah dua berarti

ya berarti tidak berarti harus dibagi

dua dibalik dan dibagi dua reaksinya ya

sedang seperti ini

hasilnya ya yang reaksi x + 3 atau 2 O2

masses tidak betah kso3 masyarakat 2002

dibalik semula Jack positif dihasilkan

hanya menjadi negatif dan tidak hanya

dibagi dua menjadi miskin 1901 Siroj

perhatikan so3 nya habis

3/2 dikurangi tengah adalah 20 21 ya

hingga reaksinya menjadi S + O2 yang

kita dari pengurangan O2 adalah satu O2

menghasilkan Respon

yang tinggal dijumlahkan yang tak hanya

biasanya sebesar mint 494 3 kilo joule

demikian contoh soal daripada

eh penerapan hukum Hess

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Hai

Baiklah kita akan membahas contoh soal

untuk yang menggunakan data entalpi

pembentukan misalnya di sini Diketahui

data entalpi pembentukan standar

untuk C3 H8 adalah mint 104 kg mol CO2 =

Min 394 kilo joule per mol H2O Meme =

Min 286 kilo joule per mol pertanyaannya

tentukan delta H reaksi untuk reaksi C3

H8 + 5 O2 menghasilkan tiga CO2 + 4 H2O

ya kita ketahui bahwa

untuk

mencari

delta H reaksi Ya kita harus bisa

membedakan mana yang reaktan dan mana

yang produk ya Mana yang reaktan dan

mana yang Produk reaktan adalah di

bagian sebelah kiri tanda panah produk

ada di sebelah bagian

Hai sebelah kanan tanda tangan Nah kita

ketahui rumus daripada

mencari delta H reaksi menggunakan data

entalpi pembentukan Standar adalah

cerita reaksi sama dengan

eh tapi pembentukan produk dikurangi

data entalpi pembentukan reaktan Nah

kita ketahui Disini yang bagian produk

adalah CO2 dan H2O jadi ikut sertakan

koefisien dari masing-masing molekul

atau senyawanya berarti tiga kali Delta

HF CO2 ditambah empat kali Delta HF H2O

min 1 ya dikurangi entalpi pembentukan

reaktan satu kali didata hfc 38 ditambah

lima kali entalpi pembentukan untuk

molekul O2 nah istrinya perlu kalian

ketahui bahwa untuk molekul gas diatomik

seperti O2 H2 ya

n2f 2C gua kayak Dua mempunyai entalpi

pembentukan

0-nya mempunyai entalpi pembentukan nol

jadi langsung dimasukkan angkanya saja

nol masukkan angkanya untuk entalpi

pembentukan CO2 Min 394 bagi tiga kali

min 394 ditambah empat kali min

286 dikurangi satu kali min 104 ditambah

lima kali nol dapat hasilnya minus

1182 kilojoule plus-minus 1144 kilojoule

ya min min 104 kilojoule ya atau data

reaksi = Min

2326 kilojoule ditambah 104 kg

didapatkan hasil akhirnya dari perubahan

entalpi reaksinya adalah mint

2222 kilojoule ya jadi seperti itu jadi

mencari entalpi reaksi hingga kalian

kurangi entalpi

Hai bukan produk dikurangi

seperti bahan entalpi pembentukan area

katanya

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Baiklah kita lanjutkan kita bahas menit

contoh soal yang menggunakan data energi

ikatan dan misalnya ada soal seperti ini

diketahui energi data energi ikatan

dalam satuan kilo joule per mol dari

ikatan CH ya tunggal

413 ko

cakap 24

195c setan rangkap

o700

99o tunggal 406

2236 pertanyaannya tentukan perubahan

entalpi ya atau delta H dari reaksi

berikut ch4 + 2 O2 menghasilkan CO2 + 2

H2O

Apa yang harus kita lakukan ya langkah

pertama yang harus dilakukan adalah

harus kita buat atau identifikasi dahulu

struktur daripada Eh senyawa-senyawa ini

yang bereaksi

seperti ini ya jadi di

buat dulu strukturnya seperti kita tahu

jenis ikatan yang terdapat di dalam

senyawa senyawa molekul yang bereaksi

seperti ini ch4cl tangannya 4 ya tunggal

sehat kemudian o2i katanya rangkap dua

ya CEO rangkap 2.2 seperti ini h2oh

tunggal ada dua seperti ini jangan lupa

koefisiennya di Tuliskan come mangada

koefisiennya ini Mbak H2O sang

ketinggalan etd2

h-o-h Oke selanjutnya

kita ketahui bahwa

eh dalam mencari entalpi reaksi ini ya

untuk menekan menggunakan data NIK

tangan berhubungan dengan pemutusan

ikatan dan pembentukan ikatan dimana

pemutusan ikatan terletak di sebelah

kiri tanda panah pembentukan ikatan

terletak di sebelah kanan tanda panah

rumusnya adalah entalpi reaksi sama

dengan jumlah energi pemutusan ikatan

dikurangi jumlah energi pembentukan

ikatan jadi ciri dikurang kanan bagian

sebelah kiri wangi sebelah kanan energi

pemutusan ikatan dikurangi energi

pembentukan ikatan kita ketahui disini

c h ada empat jadi 4 kali ikatan CH

ditambah Oh ya posisinya dua beli dua

kali

energi ikatan dengan Ungu dikurangi

disini Q nya ada dua ya dua kali

com3 tangki orang kap2 ditambah empat

kali nanya2 akan ya dua disini rupanya

kalian koefisiennya

22224 jadi ini

22244 oh nah masukkan angkanya = 4 kali

sehat berapa 413 empat kali 413 ditambah

dua kali

co.tha kap2 495 dua kali

495 ya

masukkan pakai 412 plus dua kali 455

dikurang dua kali CEO rangkap dua

799.000 dua kali 799 ditambah empat kali

soha berapa di sini 463 bertempat kali

463 tidak pohon hasilnya adalah

2600 2640

Faizul dikurang

3450 kilojoule didapatkan hasil akhirnya

entalpi reaksi tersebut adalah mint 808

meluncur ya jadi reaksi ch4 + 2 O2

menghasilkan CO2 + 2 H2O ya mempunyai

entalpi reaksi sebesar Meme 808

kilojoule itu di dalam mengerjakan atau

mencari entalpi reaksi menggunakan data

energi ikatan kalian harus memahami dulu

struktur yang terkandung dari senyawa

atau molekul yang bereaksi yang tertutup

Kenneth e

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