When hydrochloric acid is reacted with zinc heat is released. there is no external energy source such as a flame used, so where does the heat energy come from?

Explanation:

When a chemical reaction happens, the net change of enthalpy of the products and the reactants is the heat of reaction:

Then, when ∑ ΔHproducts > ∑ ΔA reactants, ΔH rxn > 0 and heat is released. This is what is called an exothermic reaction.

In an exothermic reaction, heat is released, ΔH > 0, and the surroundings will get hotter.

In and endothermic reaction heat is absorved, ΔH < 0, and the surroundings will get cooler.

alkaline metals are lithium, sodium, rubidium, potassium, cesium and francium.

alkali metals have electronegativity from 0.7 to 1, lowest in periodic table of elements, which means that alkali metals (i group in periodic table) has positive oxidation number in compounds.

electronegativity is a chemical property that describes the tendency of an atom to attract a shared pair of electrons towards itself.

alkaline metals (far left in main group) have lowest ionizations energy and easy remove valence electrons,

for example, potassium is the alkali metal and has a single valence electron in the outer electron shell.

electron configuration of potassium is: ₁₉k 1s²2s²2p⁶3s²3p⁶4s¹.

they can not exist alone in nature, because they are very reactive.

b.

the accuracy of the data.