write and simplify the closed-system energy balance Equation (Q - W = delta U+ d
ID: 514472 • Letter: W
Question
write and simplify the closed-system energy balance Equation (Q - W = delta U+ delta Ek + delta Ep) for each of the following processes, and state whether nonzero heat and work terms are positive or negative. Begin by defining the system.
c. A chemical reaction takes place in a closed adibatic ( perfectly insulated) rigid container.
d. repeat part c, only suppose that the reactor is isothermal rather than adibatic and that when the reaction was carried out adiabatically the temperature in the reactor increased.
Explanation / Answer
For a closed system, according to first law of thermodynamics,
Q - W = U + Ek + Ep
where Q is the Heat energy
W is the work energy
U is change in internal energy
Ek is change in kinetic energy
Ep is change in potential energy
c)
A chemical reaction takes place in a closed adiabatic ( perfectly insulated) rigid container.
Here,
Closed adiabatic container means there is no heat flow to or from the container i.e. Q = 0
rigid container means there is no change in volume i.e. W = 0
there is no height change mentioned,i.e. Ep = 0
system is stationary, there is no change in motion,i.e. Ek = 0
Q - W = U + Ek + Ep
0 - 0 = U + 0 + 0
U = 0
d)
repeat part c, only suppose that the reactor is isothermal rather than adibatic and that when the reaction was carried out adiabatically the temperature in the reactor increased.
Here,
there is no height change mentioned,i.e. Ep = 0
system is stationary, there is no change in motion,i.e. Ek = 0
rigid container means there is no change in volume i.e. W = 0
there is increase in temperature of reactor,i.e Q > 0
Q - W = U + Ek + Ep
Q - 0 = U + 0 + 0
Q = U
Since Q is positive, U is also positive.
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