Chemical Equations
Chemists use chemical equations to describe chemical reactions.
Word Equations
In a word equation, the reaction is written out using words to represent the reactants and products, however, the equation provides only limited information.
magnesium + oxygen → magnesium oxide
Reactants are on the left, products are on the right and the arrow means ‘goes to’ or ‘produces’. The equation would be read “Magnesium reacts with oxygen to produce magnesium oxide.”
Skeleton Equation/Unbalanced Equation
A skeleton equation shows the chemical symbols & formulae for chemicals involved in the reaction.
Mg + O2 → MgO
Notice in this skeleton equation, there are 1 Mg & 2 O atoms on the reactant side and 1 Mg & 1 O on the product side. This imbalance of O atoms makes it appear that 1 O just disappears. This cannot happen.
Balanced Equation
Chemists want to balance equations, according to the Law of Conservation of Mass (matter is neither created nor destroyed in a chemical reaction). Thus, the number of each type of element must be the same on both sides of the equation.2Mg + O2 → 2MgO
Notice in the balanced equation above, by placing coefficients of "2" in front of Mg and MgO, we have now balanced Mg (there are now two Mg atoms per side) and O (there are now 2 O atoms per side).
Before getting into the practice questions below, just a reminder how brackets and coefficients affect the number of each type of element in formulae:
TryIt! Answer: 6, 9, 27
Practice Questions
ex1. Mg + HCl → MgCl2 + H2
Tip: Typically, it’s best to leave the balancing of hydrogens (and oxygens) until the end. Start with the other elements.
ex2. H2O2 → H2O + O2
Tip: Be sure to take into account an element in all its locations if it is found in more than one reactant (or, in this case, product – notice that both products have oxygen) formula.
ex3. Ba(NO3)2 + (NH4)3PO4 → NH4NO3 + Ba3(PO4)2
Tip: If there are polyatomic ions in the chemical equation, balance the entire ion (like NO3) instead of the individual elements (like N and O).
ex4. C2H6 + O2 → CO2 + H2O
Tip: You may reach a point in balancing when you have an even number of an element (like O) on one side of the equation and an odd number of the same element on the other side of the equation. To deal with this, double the coefficients with which you have already been working.
Practice Questions Answers:
- ex1: 1, 2, 1, 1
- ex2: 2, 2, 1
- ex3: 3, 2, 3, 1
- ex4: 2, 7, 4, 6
Here's a great video that might help.
Homework:
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