A sample of gas is contained in a cylinder-and-piston arrangement.It undergoes the change in state shown in thedrawing. (a) Assume first that the cylinder and piston areperfect thermal insulators that do not allow heat to be transferred.What is the value of q for the state change? What isthe sign of w for the state change? What can be said about ΔEfor the state change? (b) Now assume that the cylinder andpiston are made up of a thermal conductor such as a metal.During the state change, the cylinder gets warmer to thetouch. What is the sign of q for the state change in this case? Describe the difference in the state of the system at the endof the process in the two cases. What can you say about therelative values of ΔE?
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.
A sample of gas is contained in a cylinder-and-piston arrangement.
It undergoes the change in state shown in the
drawing. (a) Assume first that the cylinder and piston are
perfect thermal insulators that do not allow heat to be transferred.
What is the value of q for the state change? What is
the sign of w for the state change? What can be said about ΔE
for the state change? (b) Now assume that the cylinder and
piston are made up of a thermal conductor such as a metal.
During the state change, the cylinder gets warmer to the
touch. What is the sign of q for the state change in this case?
Describe the difference in the state of the system at the end
of the process in the two cases. What can you say about the
relative values of ΔE?
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