Answer:
A chemical change occurs when the reactants chemical compositions have changed
Explanation:
a change in colour, change in temperature, change in smell, formation of a precipitate, or the formation of gas bubbles
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<h3><u>Answer;</u></h3>
HCl and KCl
<h3><u>Explanation</u>;</h3>
- Strong electrolytes are strong bases and acids.
- HCl is a strong acid; it dissociates completely to form H+ and Cl- ions. Thus, it is a strong, rather than weak, electrolyte.
- CH3COOH is acetic acid, a weak acid. Only some of it will dissociate (to H+ and acetate ions), thus, it will only be a weak electrolyte.
- NH3 will react with water as a weak base: NH3 + H2O → NH4+ + OH-. It will thus also be a weak electrolyte.
- KCl is a soluble ionic compound, and as such, it will be a strong electrolyte.
Answer:
- The standard form of a chemical element is the natural mixture of several isotopes of the same element, which is atoms with the same number of protons but different number of neutrons, while an isotope is a particular kind of atom with a definite number of neutrons.
Explanation:
A <em>chemical element</em> is a pure substance formed by atoms with the same atomic number (number of protons). This is because it is the number of protons what identifies an element.
For example: oxygen is a chemical element, so oxygen is formed by only atoms of oxygen, and the atomic number of those atoms is 8, because every oxygen atom has 8 protons.
Nevertheless, some atoms of oxygen, may have different number of neutrons. Isotopes are different kind of atoms of the same element, which only differ in the number of neutrons. So, some atoms of oxygen will have 8 neutrons, other 9 neutrons, and other 10 neutrons (those are the stable isotopes of oxygen).
That difference in neutrons, is generally accepted that, does not modifiy substantially the chemical properties of the element, but the mass number. So, the isotopes with more neutrons wil be heavier, and the isotopes with less neutrons will be lighter.
- Mass number = number of protons + number of neutrons.
In general a chemical element is formed by a mixutre of isotopes of the same element.