Laws of Thermodynamics PDF

Laws of Thermodynamics The First Law of Thermodynamics Law of Conservation of Energy  3 3 One gram of water (1 cm ) becomes 1671 cm of steam when boiled at a constant pressure of 1 5...

Laws of Thermodynamics The First Law of Thermodynamics Law of Conservation of Energy  3 3 One gram of water (1 cm ) becomes 1671 cm of steam when boiled at a constant pressure of 1 5 6 atm (1.013×10 Pa). The heat of vaporization at this pressure is L = 2.256×10 J/kg. Compute (a) v the work done by the water when it vaporizes and (b) its increase in internal energy? The heat added causes the system (water) to change phase from liquid to vapor. We can analyze this st process by using the 1 law of thermodynamics. The water is boiled at constant pressure, so we can use W = p (V – V ) to calculate the work W done by the vaporizing water as it expands. 2 1 W = p (V – V ) We are given the mass of water and the heat of 2 1 5 -6 3 -6 3 vaporization, so we can use Q = mL to calculate W = (1.013×10 Pa) (1671×10 m - 1×10 m ) v W = 169 J the heat Q added to the water. Q = mL v We can then find the internal energy change from ∆U = Q – W. -3 6 ∆U = Q – W Q = (10 kg) (2.256×10 J/kg) ∆U = 2256 J – 169 J Q = 2256 J ∆U = 2087 J The Second Law of Thermodynamics Entropy The Third Law of Thermodynamics The Absolute Zero Third Law of Thermodynamics The value of entropy of a completely pure crystalline substance is zero at absolute zero temperature. Third Law of Thermodynamics Entropy of a pure Crystal at Absolute Zero (0 K) is Zero. Third Law of Thermodynamics The entropy of a perfect crystal is zero when the temperature of the crystal is equal to absolute zero (0 K). S=0 S = k ln w where, k = Boltzmann constant = 1.38064852 × 10-23 J/K w = number of possible microstates S = k ln 1 = k (0) Third Law of Thermodynamics Absolute zero may not be able to be achieved experimentally, 2nd Law states that heat will spontaneously move from a warmer body to a colder body. The object that you are trying to cool to absolute zero will be taking in heat from the surrounding. Third Law of Thermodynamics The nebula's temperature is measured at 1 K (−272.15 °C; −457.87 °F) making it the coolest natural place currently known in the Universe. Third Law of Thermodynamics What is the purpose of the Third Law of Thermodynamics? rd 3 Law allows S to be measured for substances. The entropy of the pure substance is our zero (reference point).