Sci 401 General Chemistry PDF

SCI 401 GENERAL CHEMISTRY Lecturer: Ms. Cristine Joy M. Dalida, LPT Matter and Energy :Energy Changes in Chemical Reactions HEAT CAPACITY AND CALORIMETRY ENTHALPY SPONTANEITY 3 ENTROPY 4  Enthalpy Enthalpy is a thermodynamic quantity equiva...

SCI 401 GENERAL CHEMISTRY Lecturer: Ms. Cristine Joy M. Dalida, LPT Matter and Energy :Energy Changes in Chemical Reactions HEAT CAPACITY AND CALORIMETRY ENTHALPY SPONTANEITY 3 ENTROPY 4  Enthalpy Enthalpy is a thermodynamic quantity equivalent to the total heat content of a system. It is equal to the internal energy of the system plus the product of pressure and volume. The reaction is considered as expansion when there is a net increase in the number of moles of a gas after the reaction and conversely, it is compression if more gas molecules are consumed than are produced. 3 5  Enthalpy Enthalpy is a thermodynamic property that reflects the total heat content of a system. It is particularly useful for understanding energy changes during chemical reactions and phase transitions at constant pressure. Change in Enthalpy (ΔH) - represents the heat absorbed or released by a system during a process at constant pressure. 3 5  Types of Enthalpy Changes 1. Enthalpy of Reaction (ΔH reaction) The change in enthalpy when a chemical reaction occurs. It can be positive or negative depending on whether the reaction absorbs or releases heat. Exothermic Reaction: Releases heat, ΔH < 0 Endothermic Reaction: Absorbs heat, ΔH > 0 3 5  Types of Enthalpy Changes 2. Enthalpy of Formation The enthalpy change when one mole of a compound is formed from its elements in their standard states (1 bar of pressure and a specified temperature, usually 25°C). 3 5  Enthalpy 3. Enthalpy of Combustion The enthalpy change when one mole of a substance is completely burned in excess oxygen. **Important for determining the energy content of fuels. 3 5  Enthalpy 4. Enthalpy of Vaporization The enthalpy change required to convert one mole of a liquid into a vapor at constant pressure. 3 5  Enthalpy 5. Enthalpy of Fusion The enthalpy change required to convert one mole of a solid into a liquid at constant pressure (melting). 3 5  Enthalpy Problem #1: If 10.0 g of methane combust completely, how much energy is released? ΔH= -890.3 kJ CH4 + 2O2 CO2 + 2H2O 3 5  Enthalpy Problem #2: Determine the amount of heat associated with 1.26 x 10 g of ammonia being produced according 4 to the reaction below. ΔH= -92.6 kJ N2(g) + 3H2 (g) 2NH3(g) 3 5  Enthalpy Problem #3: Calculate the heat evolved when 87.9 g of SO2 (molar mass is 64.07 g/mol) is converted to SO 2. ΔH= -198.2 kJ 2SO2(g) + O2 (g) 2SO3(g) 3 5  Enthalpy Problem #4: Calculate the heat evolved when 266 g of white phosphorus (P4) burns in air according to the equation. ΔH= -3013 kJ P4(s) + 5O2(g) P4O10(s) 3 5  Enthalpy Problem #5: How much heat is released when 50.0 g of C2H5OH combust? ΔH= -1235 kJ C2H5OH + 3O2 2CO2 + 3H2O 3 5