TABLE 3.7 Specific Heats for Some Substances Substance cal/g °C J/g°C Elements Aluminum, Al(s) 0.214 0.897 Copper, Cu(s) 0.0920 0.385 Gold, Au(s) 0.0308 0.129 Iron, Fe(s) 0.108 0.452 Silver, Ag(s) 0.0562 0.235 Titanium, Ti(s) 0.125 0.523 Compounds Ammonia, NH,(g) 0.488 2.04 Ethanol, C,H,0(1) 0.588 2.46 Sodium chloride, NaCI(s) 0.207 0.864 Water, H;O(1) 1.00 4.184 Water, H,O(s) 0.485 2.03
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.
| When a substance with a mass of 45.6 g absorbs 575 J, its temperature increases from 21 °C to 35 °C. Calculate the specific heat, in J/g °C, of the substance. Identify the substance from Table 3.7. |
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