Answer:
C) It is the reactant that is left over after the reaction stops.
Explanation:
The excess reactant is the reactant that is left over after the reaction stops. The extent of the reaction is not determined by this reactant.
A limiting reactant is a reactant that is in short supply within a given reaction.
Such reactants determines the extent of chemical reaction.
- Limiting reactants are used up in a chemical reaction.
- The excess reactants remains unchanged after the reaction.
Answer:
A. there is an isotope of lanthanum with an atomic mass of 138.9
Explanation:
By knowing the different atomic masses of both Lanthanum atoms, we can not tell anything about their occurence in nature. Therefore, all the last three options are incorrect. Because, the atomic mass does not tell anything about the availability or natural abundance of an element.
Now, the isotopes of an element are those elements, which have same number of electrons and protons as the original element, but different number of neutrons. Therefore, they have same atomic number but, different atomic weight or atomic masses.
Hence, by looking at an elements having same atomic number, but different atomic masses, we can identify them as isotopes.
Thus, the correct option is:
<u>A. there is an isotope of lanthanum with an atomic mass of 138.9.</u>
D. a compound can only be separated into its components by chemical means
