Complete the following sentences:

a In an exothermic reaction, the energy transferred to the surroundings from forming new bonds is than the energy needed to break existing bonds.

b In an endothermic reaction, the energy transferred to the surroundings from forming new bonds is than the energy needed to break existing bonds.

c The energy change of an exothermic reaction has a sign.

d The energy change of an endothermic reaction has a sign.

Explanation:

a) In an exothermic reaction, the energy transferred to the surroundings from forming new bonds is ___more than the energy needed to break existing bonds.  

b) In an endothermic reaction, the energy transferred to the surroundings from forming new bonds is ___less than the energy needed to break existing bonds.  

c) The energy change of an exothermic reaction has a negative sign.  

d) The energy change of an endothermic reaction has a positive sign.

The energy changes occur during the bonds formation and bonds breaking.

There are two types of reaction endothermic and exothermic reaction.

Endothermic reactions:

The type of reactions in which energy is absorbed are called endothermic reactions.

In this type of reaction energy needed to break the bond are higher than the energy released during bond formation.

For example:

C + H₂O   →  CO  + H₂

ΔH = +131 kj/mol

it can be written as,

C +  H₂O  + 131 kj/mol  →  CO  + H₂

Exothermic reaction:

The type of reactions in which energy is released are called exothermic reactions.

In this type of reaction energy needed to break the bonds are less than the energy released during the bond formation.

For example:

Chemical equation:

C + O₂   →  CO₂

ΔH = -393 Kj/mol

it can be written as,

C + O₂   →  CO₂ + 393 Kj/mol

the answer is na (sodium)

answer:

technetium is the most reactive. this is followed by silver. the least reactive out of these three elements is strontium.