Determine whether each of the following is exothermic or endothermic and indicate the sign of δh.
a. dry ice evaporating
b. a sparkler burning
c. the reaction that occurs in a chemical cold pack often used to ice athletic injuries

Explanation:

There are two type of reaction possible , i.e. , exothermic and endothermic reaction ,

Exothermic reaction -

The type of reaction in which energy in the form of heat or light is released , is known as exothermic reaction ,

The reaction mixture usually get heated after the reaction .( temperature increases ) .

The sign of ΔH of an exothermic reaction is negative .

Similarly ,

Endothermic reaction -

The type of reaction in which energy is absorbed in the form of heat is known as endothermic reaction .

The reaction mixture usually get cooled after the reaction .( temperature decreases ) .

The sign of ΔH of an Endothermic  reaction is positive .

a. dry ice evaporating ,

Endothermic reaction , ΔH = positive .

b. a sparkler burning ,

Exothermic reaction ΔH = negative .

c. the reaction that occurs in a chemical cold pack often used to ice athletic injuries

Endothermic reaction , ΔH = positive .

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.

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