Section 1 Section 2 Heat capacity is defined as the amount of energy needed to raise the Enthalpy, AH is defined as the change in internal energy, AU, plus pAV or temperature of a specific object by 1 C or 1 K. The unit of heat capacity is the work done by pressure on the system. This looks like: AH = AU + PAV c K ' We can also use a more generalized form of this concept, called A indicates a change or the difference between an initial condition and a final condition such as: AV= VF-Vi specific heat capacity, which is defined as the amount of energy needed to raise the temperature of 1 gram of a material by 1 C or 1 K. The unit of AU, internal energy, is the sum of heat, q, and the work done on the specific heat capacity is - g.c or surroundings by the system, -PAV. g.K AU = q -PAV 1. What is the heat capacity of 2.0 liters of water? Therefore, at constant pressure AH = q specific heat of water= 4.18 J gri C-1, density of water = 1.0 g/ml There are multiple ways to calculate AH for a reaction, AH, Hess's law or bond energy. 1. AH, Enthalpy of Formation 2. How much heat is necessary to raise the temperature of 1.5 L of water 4 NH3(9) + 502(9) - 4 NO(g) + 6 H20(9), 25.C 1 atm from 37.0 C to 42.0.C? Allproducts - AHreactants Compound AH Of NH 3 (9 ) -45.56 kj/mol 90.25 kJ/mol The principle of thermal equilibrium is based on the idea that energy cannot NO (9) be created or destroyed. This means that in a closed system, a system H2O (9) -241.8 kj/mol where energy isn't lost to the surroundings, all energy lost by one component of the system will be gained by the other component/s of the system. Mathematically, this is represented by: qlost = -qgained 3. A 1.05 kg steel sword at 850 C is submerged in a 115L tank of water at 30 C. What is the final temperature of the water if the specific heat of steel is 0.466 J.g-1. C-1 and the specific heat of water is 4.18 ] g-1 C-12. Hess's Law 4 NH3(g) + 502(9) > 4 NO(g) + 6 H20(g), N2(g) + 02(g) > 2NO(g) AH= -180.5 K] NZ(g) + 3H2(g) > 2NH3(g) AH= -91.8 kJ 2H2(g) + 02(9) > 2H20(g) AH= -483.6 k] 3. Bond Energy 4 NH3(g) + 502(9) > 4 NO(g) + 5 H20(g), kJ/mol 391 498 607 463 S_e_cti_on_3 The ideal gas law uses the equation: PV = nRT Hot air balloons operate by heating air to achieve a lower density for the gas inside the balloon than the density of the surrounding air. 1. A balloon with a volume of 2.5x106 L is heated to 275C at standard atmospheric pressure (1.0 atm). How many moles of air are present in the balloon? 2. If the molar mass of air is 28.97 g/mol, what is the density of the gas inside the balloon in kg/L? 3. What is the density (kg/L) of 1.0 L of air at 75F and 1 atm? 4. What is the density (kg/L) of 1.0 L of air at 50F and 1 atm? 5. Balloons fly when the density of the gas inside of the balloon ' less than the density of the gas outside of the balloon. Is it b launch a balloon in the morning when temperatures are coole afternoon when temperatures are warmer