A substance is characterized by the thermodynamic data below. Using this, determine the amount of heat (in kJ) required to warm 125.0 grams of the substance from 4.2°C to its melting point, and then completely melt it. Cs, solid 1.92 J/g°C Cs, liquid 3.14 J/g°C Cs, gas 1.59 J/g°C ∆H fus 4.89 kJ/mol ∆H vap 50.88 kJ/mol Melting point 42.5°C Boiling point 176.2°C Molar mass 159.4 g/mol
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.
Question 17
A substance is characterized by the
| Cs, solid | 1.92 J/g°C |
| Cs, liquid | 3.14 J/g°C |
| Cs, gas | 1.59 J/g°C |
| ∆H fus | 4.89 kJ/mol |
| ∆H vap | 50.88 kJ/mol |
| Melting point | 42.5°C |
| Boiling point | 176.2°C |
| Molar mass | 159.4 g/mol |
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