Answer:
w = -531 kJ
1. Work was done by the system.
Explanation:
Step 1: Given data
- Heat gained by the system (q): 687 kJ (By convention, when the system absorbs heat, q > 0).
- Change in the internal energy of the system (ΔU°): 156 kJ
Step 2: Calculate the work done (w)
We will use the following expression.
ΔU° = q + w
w = ΔU° - q
w = 156 kJ - 687 kJ
w = -531 kJ
By convention, when w < 0, work is done by the system on the surroundings.
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Explanation:
Ethanol can be oxidized to ethanal or acetaldehyde which is further oxidized to acid that is acetic acid.
→
[oxidation by loss of hydrogen]
-
An oxidizing agent potassium dichromate(VI) solution is used to remove the hydrogen from the ethanol.
- An oxidizing agent used along with dilute sulphuric acid for acidification.
Acetaldehyde can also be reduced back to ethanol again by adding hydrogen to it by using a reducing agent that is sodium tetrahydro borate, NaBH4.
- The oxidation of aldehydes to carboxylic acids can be done by the two-step process.
- In the first step, one molecule of water is added in the presence of a catalyst that is acidic.
- There is a generation of a hydrate. (geminal 1,1-diol).
→
[reduction by the gain of electrons]
Here, the oxidizing agent used is
in the presence of acetone.