I am asked this question:

Write a balanced equation, including state symbols, for this reaction:

$\ce{calcium + hydrochloric acid -> calcium chloride + hydrogen}$

I answered this:

$\ce{Ca(s) + 2HCl(aq) -> CaCl2(s) + H2}$

This was the correct answer:

$\ce{Ca(s) + 2HCl(aq) -> CaCl2(aq) + H2}$

I thought that the $\ce{CaCl2}$ was a solid precipitate (ppt.) instead of aqueous(aq).

Here are the known chemical states:

  • solid(s)
  • liquid(l)
  • gas(g)
  • aqueous solution(aq)

Is there any method to work out the chemical state of a reactant or product in a chemical equation, if I know the chemical states of all of the other reactants?


According to these basic solubility rules:

enter image description here

Calcium chloride (CaCl2) is soluble. Hence, you write CaCl2(aq) in the equation.

  • 1
    $\begingroup$ Generalised tables like this should be taken with a pinch of salt. Sodium Bismuthate, for one, is an insoluble sodium salt. $\endgroup$ Jan 15 '20 at 2:07

You must first learn two things before hoping to solve any chemical problem:

  1. You must learn how to write a balanced equation, with the correct numbers of atoms, before guessing about their physical state. For example, in your first equation, there is one $\ce{Ca}$ on the left-hand side and $\ce{2 Ca}$ at the right-hand side. This is not balanced.

  2. You should realize that $\ce{CaCl}$ and $\ce{CaCl2}$ are not the same substance. When you say that you "typed $\ce{CaCl(s)}$ instead of $\ce{CaCl(aq)}$" you still are wrong. You should have said, "instead of $\ce{CaCl2(aq)}$".

Now to answer your question, there is no way of obtaining the physical state from the periodic table.

Simply speaking, you should here know that pure $\ce{HCl}$ is a gas at room temperature, and it is very soluble in water. In the pure state, $\ce{HCl}$ is called hydrogen chloride. Dissolved in water, $\ce{HCl}$ is called hydrochloric acid.

  • 1
    $\begingroup$ Thank you for trying to help me. I’m still unclear about this issue and would be grateful if you could help me understand the rest of my question, which is, how to work out the chemical state of CaCl when I know the state of the reactants and products ? $\endgroup$
    – mfsg
    Jan 14 '20 at 21:05
  • $\begingroup$ CaCl does not exist. $\endgroup$
    – Maurice
    Jan 14 '20 at 21:12
  • 1
    $\begingroup$ I’m sorry, I meant CaCl2. So my question is, how to work out the chemical state of CaCl2 when I know the state of the reactants and products? $\endgroup$
    – mfsg
    Jan 14 '20 at 21:24
  • 1
    $\begingroup$ You cannot. Not from the basic principles. You can use as a guidance the provided table,but it covers just a minor part of substances and there are exceptions. Additionally, the state may depend on quantitative circumstance. There is lot of empirical knowledge in chemistry. $\endgroup$
    – Poutnik
    Jan 15 '20 at 8:04

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