thermodynamics : introduction and first law
DESCRIPTION
Presentasi mata kuliah termodinamika material dengan menyangkut materi pengenalan termodinamika dan hukum pertama termodinamika yang akan berhubungan dengan termodinamika material.TRANSCRIPT
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Thermodynamics : Introduction And First
LawMuhammad Joshua YB (1406563866) - 36
Muhammad Al-Wafiy (1406563866) - 35
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Pendahuluan
Termodinamika merupakan bidang ilmu yang mempelajari kesetimbangan yang terjadi terhadap system dan akibat-akibat dari pengaruh luar (energy).
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Koordinat Sistem• Koordinat system merupakan variable-variable yang
mempengaruhi keadaan dari system.Variabel-variable ini terbagi menjadi dua :1.Intensive VariableAdalah variable yang tidak tergantung pada ukuran system : P,T2.Extensive Variable Adalah variable yang tergantung pada ukuran system : V, massa, energy, mol.
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Harga Jenis dan Harga Jenis MolarHarga jenis dirumuskan sebagai berikut :
Sedangkan Harga jenis molar dirumuskan sebagai berikut :
Karena, n = ,
maka V* = M=
Dan, V = =
Sehingga , V* = V.Mr
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Interaksi
• Thermal• Mekanik• Kimia
Materi
Energi
Terbuka
Tertutup
Terisolasi
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Energi Dalam
Untuk system gas ideal, energy dalam sama dengan jumlah energy kinetic
Contoh translasi, rotasi, vibrasi, electrostatic.
U = P V f = derajat kebebasan
Monoatomik : f = 3
Diatomik : f = 5
Poliatomik : f = 6
ΔU = U2 – U1
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Kapasitas panas dan kalor spesifik
• Kapasitas panas ( C ) : C = q = C (T2 . T1)
Cv = at constant volume
Cp = at constant pressure
dU = Cv dT
dH = Cp dT Cp – Cv = R• Kalor spesifik (c) : c =
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Fungsi ProsesReversible = terjadi sangat lambat, keadaan setiap prosesnya dapat dianggap setimbang.Irreversible = terjadi sangat cepat, kesetimbanga hanya terjadi pada kondisi-kondisi tertentu.
Irreversible : Pex < Pgas (ekspansi) Pex > Pgas (kompresi)
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Fungsi Proses
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Persamaan Gas Ideal
• PV = nRTP = pressure (atm)V = Volume (Litre)n = molR = konstanta, 8.314 joule/mol K atau 0.08206 L.atm/mol
KT = temperature (K)
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Constant Volume Process (isokhorik)
Karena volume konstan, maka w = 0Sehingga,
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Constant Pressure Process (isobaric)
Hint : Jika dan hanya jika prosesnya reversible
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Reversible Adiabatic Process
Adiabatik merupakan proses yang apabila terjadi tanpa perpindahan panas dan massa antara system dan lingkungan.
У =
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Reversible Isothermal Process
Karena perubahan suhu sama dengan nol, maka perubahan energy dalam juga nol, sehhingga :
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Soal 1
• Suatu gas ideal pada 300 K memiliki volume 15 liter pada tekanan 15 atm. Hitung (1) volume akhir system, (2) kerja yang dilakukan system. Jika system mengalami ekspansi isothermal ke tekanan 10 atm
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Jawaban
Dik : T1 = 300 K, V1 = 15 L , P1 = 15 atm, P2 = 10 atm
(1) V2 = = = 22.5 liter
n = = = 9.1 mol
2) w = nRT ln = 9.1 x 8.314 x 300 x ln = 9203 joule
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Soal 2
• Suatu gas ideal pada 25 0C memiliki volume 10 liter pada tekanan 10 atm. Hitung (1) volume akhir system, (2) kerja yang dilakukan system. Jika (a) system mengalami ekspansi isothermal ke tekanan 15 atm dan (b) system mengalami proses adiabatic reversible ke tekanan 15 atm. Cv = 1.5 R
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Jawaban
Dik : T1 = 25 + 273 = 298 K, V1 = 10 L , P1 = 10 atm, P2 = 15 atm
Soal (a)
(1) V2 = = = 6.7 liter
n = = = 4.1 mol
2) w = nRT ln = 4.1 x 8.314 x 298 x ln = - 4119 joule
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Soal (b)
Cp = R + (1.5 R) = 2.5 R , y = = , 1/y = 3/5
(1) V2 = ( = 7.8 liter
T2 = = 348 K
(2) w = nCv (T2-T1) = 4.1 x 8.314 x 1.5 x (348 – 298) = 2556 joule = 2.5 kilojoule
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Soal 3
10 liter gas ideal monoatomic pada 25°C dan tekanan 10 atm, mengalami keadaan adiabatic sampai dengan tekanan 2 atm. Kemudian mengalami keadaan isobaric sampai dengan volume awal. Dan mengalami isokhorik sampai kembali ketekanan semula. Hitunglah total kerja yang dilakukan system ! Cv = 1.5 R
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Jawaban
Dik : P1 = 10 atm , P2 = 2 atm , V1 = 10 liter , T1 = 25 + 273 = 298 K
Cp = R + (1.5 R) = 2.5 R , y = = , 1/y = 3/5
n = = = 4.1 mol
V2 = ( = 26.3 liter
T2 = = =156 K
w1 = nCv (T2-T1) = 4.1 x 8.314 x 1.5 x (156 – 298) = - 7261 joule = -7.3 kilojoule
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Jawaban
w2 = P (V1-V2) = 2 x ( 10 – 26.3) = -32.6 = -33 joule
W-total = w1 + w2 = -7300 + (-33) = -7333 joule
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The End
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Referensi
• Gaskell, David R. 2003. Introduction To The Thermodynamics Of Materials, 4th edition . Taylor francis.