A process is carried out at constant pressure. Given that ΔE is positive and ΔH is negative,
Select one:
A. the system absorbs heat and contracts during the process.
B. the system absorbs heat and expands during the process.
C. the system loses heat and contracts during the process.
D. the system loses heat and expands during the process.
dE = q+w = dH-p(V2-V1)
If dE is + and dH is -, then w MUST be + so -p(V2-V1) must be +
With dH is - then heat must be released. That means A and B can't be right. The answer must be C or D. To make -p(V2-V1) +, must V2 or V1 be the larger number? If V2>V1, the w is -. If V2<V1, then w is +. So does the system expand or contract?
The correct answer is C. the system loses heat and contracts during the process.
When ΔE is positive, it means that the internal energy of the system has increased. And when ΔH is negative, it means that the enthalpy of the system has decreased.
In a process carried out at constant pressure, a negative change in enthalpy (ΔH) indicates that heat is being released from the system. Therefore, the system loses heat.
When a system loses heat, its temperature decreases. As a result, the particles in the system have less energy and move slower, causing the system to contract.
To determine the correct answer, let's break down the information provided.
First, ΔE represents the change in internal energy of the system. If ΔE is positive, it means that the system has gained energy.
Second, ΔH represents the change in enthalpy of the system. If ΔH is negative, it means that the system has lost heat.
Given that the process is carried out at constant pressure, this tells us that the heat exchange is mainly due to changes in the internal energy of the system, rather than work done by or on the system.
Now, let's think about the options provided:
A. the system absorbs heat and contracts during the process.
B. the system absorbs heat and expands during the process.
C. the system loses heat and contracts during the process.
D. the system loses heat and expands during the process.
Since ΔE is positive, it means the system is gaining energy. This rules out options C and D, which both involve the system losing heat.
Since ΔH is negative and the process is carried out at constant pressure, it implies that the heat absorbed is greater than the work done by the system to expand. Therefore, the system is doing work on the surroundings and expanding.
Based on these considerations, the correct answer is option B: the system absorbs heat and expands during the process.