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Chemical Equations

Chemical Equations. Chemical Equation: A method of representing reactants and products of a reaction by showing the formulas. Example: 2H 2 + O 2 → 2H 2 O In the reaction above, we can see that hydrogen reacts with oxygen to form water. Writing Chemical Equations.

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Chemical Equations

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  1. Chemical Equations

  2. Chemical Equation: A method of representing reactants and products of a reaction by showing the formulas. Example: 2H2 + O2→ 2H2O In the reaction above, we can see that hydrogen reacts with oxygen to form water.

  3. Writing Chemical Equations • The simplest form of a chemical equation is called the nominative equation (in this type of equation we use words, not symbols) hydrogen + oxygen water • The + sign means “ reacts with” • The arrow means “ to produce”

  4. However, the nominative formula tells you nothing about the composition (formulas) of the reactants and products… So, a better formula is : H2 + O2 H2O (skeleton eqtn) Can you notice anything wrong with the equation above? (look at the number of atoms involved)

  5. There are some elements that are always found in groups of two if they are not bonded with other elements. These include: H N O F Cl Br I Groups of these atoms are called DIATOMIC MOLECULES

  6. To balance an equation we need to consider the Law of Conservation of Mass • The Law of Conservation of Mass states that the mass of the reactants in a chemical equations must equal the mass of the products. • So, lets consider again H2 + O2 H2O How many hydrogen and oxygen atoms in the a) reactants? b) products?

  7. Balancing Equations… • You need to add coefficients to balance the equation…to make sure that there are the same number of atoms of each kind on both sides.

  8. Sometimes, you must indicate the state of the reactants and products… • For solids add (s) after the element symbol ex. Fe (s) • For liquids add (l), ex. H2O (l) • For gases, add (g), ex. O2 (g) • For a substance dissolved in water (aq) ex. NaCl (aq) (aq represents “aqueous” which is latin for “in water”)

  9. Here is what magnesium + oxygen would look like:

  10. The following are examples of balanced equations: • H2 + Cl2 2HCl • Zn + 2HCl ZnCl2 + H2 TIP: Create a Reactants / Products Chart to see whether the number of atoms of each element are equal on both sides of the equation

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