Asubstance that could be separated into two or more substances only by a chemical change is a(n)

Compound  

Explanation:

A compound is a substance that can be separated into two or more substances only by a chemical change.

For example, water is a compound.

We can separate it into hydrogen and oxygen by electrolysis.

answer: enthalpy

explanation:

for a exothermic reaction, the energy is released i.e. the energy of the products is lower than the energy of the reactants.

= enthaply

= energy of products

= energy of reactants

as , thus comes out to be negative. negative value of enthalpy shows that the reaction is exothermic.

the density of gold = 19.3 g/cm3

the relation between density and mass and volume is

density = mass / volume

given :

mass of gold = 13 g

density = 13g / volume = 19.3

volume = 13 /19.3 = 0.67 cm^3

thus volume of gold nugget = 0.67 cm^3