Equal amounts of four different substances (A-D) where added separately to equal amounts of an acid and a thermometer placed in the mixture. For which substance is the reaction the most endothermic?

A. temperature rises by 5oC
B. temperature falls by 3oC
C. temperature rises by 3oC
D. temperature falls by 5oC

D

Explanation:

An endothermic reaction is one in which there is a temperature fall and the reaction vessel becomes colder. For example, adding potassium iodide crystal to water in a beaker, the beaker becomes cold.

Now, to the question: The most endothermic reaction is the one with the largest temperature drop

A is wrong, temperature rises , it is exothermic

B is endothermic but not correct

C is wrong, temperature rises, it is exothermic

D is correct, temperature falls, It is endothermic and has the largest temperature drop, so we pick it

the mass of the cathode increases because ions from the solution get reduced to atoms and become part of the cathode.

explanation:

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explanation:

metals have excess of electrons whereas non-metals have deficiency of electrons. thus, in order to gain stability metals easily donate their electrons to the non-metals.

for example, electronic configuration of sodium is and electronic configuration of phosphorous is .

when a phosphorous atom and sodium atom combine together then sodium will donate is extra one electron to the phosphorous atom. as a result there will be formation of ionic bond between sodium and phosphorous.

the reaction will be as follows.

there, are three sodium sodium atoms and each of them will donate its one extra electron to phosphorous atom. thus, the sub-shell of phosphorous gets completely filled.  

thus, we can conclude that electrons are transferred from atoms of sodium to atoms of phosphorous. this transfer makes the sodium atoms donate one electron and the phosphorous atoms to gain one electron. as a result, the sodium and phosphorus atoms strongly attract each other.