Endothermic reaction, and surrounding?

[babowc]

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Q189 on Destroyer GC says that:
"during an endothermic reaction, the temperature of the SURROUNDINGS is lowered"

Isn't the SYSTEM temperature lowered, not the surrounding?

I understand that the system will absorb heat from the surrounding, is that why it lowers the surrounding temperature?...

 

[J777]

Your last sentence is correct. In absorbing heat, the system gets hotter in endothermic rxns. Essentially, it is removing heat from the surroundings, which is why the surroundings get colder

 

[babowc]

Relating to this subject.. how does this passage from Destroyer make sense?

GC Q57. When solid NH4NO3 is dissolved in water at 25*C, the solutino temperature decreases. This reaction is endothermic

It goes against what you said, J777, yet the solution says it's a true statement.
If the reaction is endothermic, it's absorbing/using heat, so wouldn't it make sense that the system gets warmer and the surrounding gets cooler?

 

[J777]

This concept can be quite confusing. The above Destroyer explanation is correct also.

There is a very important distinction between a system and its surroundings. The system can be thought of as the reaction itself (what you would see in a balanced chemical equation). It is kind of arbitrary, but I like to think of it as the reaction. The surroundings are everything else not included in the system. The system is absorbing heat from the surroundings.

In this problem, the system is defined as the salts that are dissolving. The surroundings are everything else, which includes the water within the solution. The system requires energy for the dissolving to occur. Heat is being absorbed from the surroundings (the water, air container....) so that that the salt can separate into ions and dissolve. That is why the temperature of the solution decreases during the endothermic reaction.

To help illustrate the concept, let's look at the opposite concept, exothermic reactions (such as combustion). During combustion, the system loses heat and emits it to the surroundings. As a result, the surroundings actually get hotter (think engines burning fuel).

 

[babowc]

Ah.. That makes sense if the reaction between the salts is considered the "system".
Thanks for the clarification!