Which of the following forms a new substance? melting, evaporating, freezing or burning

burning

Explanation:

Burning or combustion is a chemical change. Hydrocarbon in the presence of oxygen burns to form carbon dioxide and water. In chemical change reactants react with one another to form new products. In chemical change the chemical composition and chemical property  of the reactants and products and different from each other.

In a physical change there is only a change in the phase of the substance no new substance is formed. Melting, evaporating, freezing are all phase changes hence they are all physical changes.

given:

mass of na = 115 g

excess cl2

to determine:

mass of nacl produced

explanation:

given reaction is-

2na(s) + cl2(g) → 2nacl(s)

since cl2 is in excess, na will be the limiting reagent

as per the reaction stoichiometry na: nacl = 1: 1

i.e. moles of na reacted = moles of nacl formed

now, # moles of na = mass of na/atomic mass

                                  = 115 g/23 g.mol-1 = 5 moles

therefore, moles of nacl = 5

molar mass of nacl = 58 g/mol

mass of nacl = 5 moles * 58 g.mol-1 = 290 g

ans: amount of nacl produced = 290 g