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 .

the density(ratio between mass and volume as m/v) decreases from top to bottom in periodic table group as the size increases and nuclear charge decreases. but in periods density increases from left to right as atom size decreases and nuclear charge increases.