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secondary 4 | Chemistry
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Annela
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Annela

secondary 4 chevron_right Chemistry chevron_right Singapore

This is exothermic graph.I understand the intersection point means the reaction end but why the temperature decreases? Is it decreases to room temperature?

Aso for endothermic graph, the temperature decreases but yet increases again?

Can someone explain to me why so?

Date Posted: 1 week ago
Views: 6
Eric Nicholas K
Eric Nicholas K
1 week ago
Good evening Annela!!!

The reaction starts out at room temperature and rises in temperature (being exothermic). Once the reaction concludes, there is no more release of heat energy from the reaction. Eventually, hot air spreads to cooler areas by diffusion to allow the temperature between the reaction and the surroundings to reach an equilibrium temperature.

It’s a similar idea for the endothermic version.

Think of why the water in a kettle cools down after boiling.
J
J
1 week ago
I'll say it's more of the heat lost to the cooler surrounding air rather than any diffusion taking place. The heat is only causing the air to expand

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Arnold K H Tan
Arnold K H Tan's answer
880 answers (A Helpful Person)
1st
Unfortunately, both J's and Eric's comments are incorrect for the short time frame of a titration experiment.
Arnold K H Tan
Arnold K H Tan
1 week ago
The excess KOH added after the end point for the reaction, cools the solution. KOH is at room temperature. Similarly for endothermic reaction, the lowest temperature (below ambient room temperature) indicates when the limiting reactant has been used up. As more of the excess reactant is added, the temperature rises to room temperature, as the excess reactant added is at room temperature.
Eric Nicholas K
Eric Nicholas K
1 week ago
Interesting. I took it that the horizontal axis was time and KOH was added to neutralisation/equivalence point. If excess KOH is added then yes, the KOH’s room temperature is a more significant factor than the air’s room temperature.

Arnold’s solutions are correct since the horizontal axis represents the volume of KOH added and not time.

Annela, I suggest an “extrapolation” of the straight lines by dotted lines instead of solid lines.