C, gas Step A: How much heat energy (in kJ) must be absorbed to increase the temperature of the solid from -14.8 °C to the melting temperature?
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.
Solution
From the heating curve, it is clear that the substance is solid at 
and the melting point of the substance is 
. The substance begins to melt at this temperature and temperature remains constant till the substance is completely converted to liquid. Once the liquifaction is complete, the temperature of the substance rises till its boiling point, 
. The change of state from liquid to gas begins at this temperature and temperature remains constant till the substance is completely converted into gas. Once the vapourisation is complete temperature of the substance increases when heat is supplied.
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