1. When a 6.50 g sample of solid sodium hydroxide dissolves in 100.0 g of water in a coffee- cup calorimeter, the temperature rises from 21.6 °C to 37.8 °C. Calculate AH (in kJ/mol NaOH) for the solution process NAOH(s) Na*(aq) + OH¯(aq) > Assume that the specific heat of the solution is the same as that of pure water. 2. A 7.35 g sample of quinone (C6H4O2) is burned in a bomb calorimeter whose total heat capacity is 7.854 kJ/°C. The temperature of the calorimeter increases from 18.75 °C to 39.67 °C. What is the heat of combustion per gram of quinone? Per mole of quinone? 3. From the enthalpies of reaction → 2 HF(g) AH = -537 kJ H2(8) + F2(g) C(s) + 2 F2(8) AH = -680 kJ CF4(g) CH4(g) calculate AH for the reaction of ethylene with F2: > 2 C(s) + 2 H2(8) AH = +52.3 kJ - C2H4(g) + 6 F2(g) 2 CF4(g) + 4 HF(8) 4. Calcium carbide (CaC2) reacts with water to form acetylene (C2H2) and Ca(OH)2. From the following enthalpy of reaction data and data in Appendix C, calculate AH,° for CaC2(s): CaC2(s) + 2 H,O(1) Ca(OH)2(s) + C,H½(g) - AH° = -127.2 kJ 5. Calculate AS° values for the following reactions by using tabulated S° values from Appendix C. In each case explain the sign of AS°. (a) HNO3(g) + NH3(8) (b) 2 Fe¿O3(s) (c) CaCO;(s,calcite) + 2HCI(g) NH4NO3(s) 4 Fe(s) + 3 O2(g) - > CaCl2(s) + CO2(8) + H20(1) (d) 3 CaHde) → CH(/) + 6 Halg)
Thermochemistry
Thermochemistry can be considered as a branch of thermodynamics that deals with the connections between warmth, work, and various types of energy, formed because of different synthetic and actual cycles. Thermochemistry describes the energy changes that occur as a result of reactions or chemical changes in a substance.
Exergonic Reaction
The term exergonic is derived from the Greek word in which ‘ergon’ means work and exergonic means ‘work outside’. Exergonic reactions releases work energy. Exergonic reactions are different from exothermic reactions, the one that releases only heat energy during the course of the reaction. So, exothermic reaction is one type of exergonic reaction. Exergonic reaction releases work energy in different forms like heat, light or sound. For example, a glow stick releases light making that an exergonic reaction and not an exothermic reaction since no heat is released. Even endothermic reactions at very high temperature are exergonic.
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