Writing Word Equations
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practice worksheets
Ever wonder how to translate a chemical
reaction from a written statement in regular English to equation form?
Here's how, using the example below:
Example: When calcium hydroxide reacts with hydrochloric acid in water, dissolved calcium chloride and water are formed. This reaction gives off heat.
Step 1: Write the unbalanced equation by translating the written names into chemical formulas In this case, the formulas you need to know are those for calcium hydroxide, hydrochloric acid, calcium chloride, and water. When you translate these into their formulas, you should get the unbalanced equation: Ca(OH)2 + HCl --> CaCl2 + H2O If you've forgotten how to write formulas, visit here for more info about writing formulas for ionic compounds and here for writing formulas for covalent compounds. Step 2: Balance the equation You need to balance the equation to ensure that the chemical reaction follows the law of conservation of mass, which says that you've got to have the same number of atoms of each element on both sides of the equation. I'll assume for the purposes of this activitiy that you know how to balance equations. If you don't, try visiting here for help. For this reaction, the equation, when balanced, looks like this: Ca(OH)2 + 2 HCl --> CaCl2 + 2 H2O Step 3: Figure out the states of each of the chemicals in the equation "States" refers to the form in which you can find a chemical. The states you need to worry about are solid, liquid, gas, and aqueous. Solid, liquid, and gas are probably familiar to you, and "aqueous" is just a fancy word for "dissolved in water". The symbol for a solid is (s), liquid is (l), gas is (g), and aqueous is (aq). You need to make sure you write these in the parentheses, and that you write them right after the formulas in the same place and size that you put the subscripts in the formulas. Check out the example below to see what I mean. Now, the big question is this: How can you tell if something is a solid, liquid, gas, or aqueous? Here are some guidelines that might help you:
So, let's take a look at our equation: (In case you forgot what it was, it was Ca(OH)2 + 2 HCl --> CaCl2 + 2 H2O
Putting all this stuff together, we get the following equation: Ca(OH)2(s) + 2 HCl(l) --> CaCl2(aq) + 2 H2O(l) Step 4: Sticking all the other relevant symbols in here somewhere The last thing we need to do is to stick a bunch of other symbols around here to indicate other relevant things about the reaction. These relevant things may include reaction conditions (things you need to do to make the reaction take place) or indications about whether the reaction is exothermic (gives off heat and feels hot) or endothermic (absorbs heat and feels cold). Here's a list of the symbols you may need to use:
In the reaction we were given, nothing much was said except that the reaction gives off heat, meaning that it's an exothermic reaction. As a result, the only symbol we really need is a DH symbol. Since the amount of heat given off wasn't specified, all we can do is say that DH is negative. As a result, our equation looks like this: Ca(OH)2(s) + 2 HCl(l) --> CaCl2(aq) + 2 H2O(l) DH = - And that's all you need to do! |
Questions? Comments? Email them to me at misterguch@chemfiesta.com