Multiple Choice
A system receives 575 J of heat and does 425 J of work on the surroundings. Calculate the change in the internal energy, ΔE, of the system.
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8. Thermochemistry
First Law of Thermodynamics
Multiple Choice
When a chemical process is reversed, how do the magnitude and sign of the enthalpy change (ΔH) compare to the original process?
A
The magnitude increases, and the sign is reversed.
B
Both the magnitude and the sign remain the same.
C
The magnitude decreases, but the sign remains the same.
D
The magnitude remains the same, but the sign is reversed.
Verified step by step guidance1
Understand that enthalpy change (\$\(\Delta\) H\$) is a state function, meaning it depends only on the initial and final states of a process, not on the path taken.
Recognize that when a chemical process is reversed, the initial and final states swap places, so the enthalpy change for the reverse process must have the same magnitude but opposite sign.
Express this relationship mathematically as: \$\(\Delta\) H_{reverse} = -\(\Delta\) H_{forward}\$.
Note that the magnitude (absolute value) of \$\(\Delta\) H\$ remains unchanged because the energy difference between the states is the same regardless of direction.
Conclude that the correct description is: the magnitude remains the same, but the sign of \$\(\Delta\) H\$ is reversed when the process is reversed.
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