How molecules are symbolized Cl 2 2Cl 2Cl 2 Molecules may also have brackets to indicate numbers of atoms. E.g. Ca(OH) 2 O H O H Ca Notice that the OH is a group The 2 refers to both H and O

How many of each atom are in the following? a) NaOH b) Ca(OH) 2 c) 3Ca(OH) 2 Na = 1, O = 1, H = 1 Ca = 1, O = 2, H = 2 Ca = 3, O = 6, H = 6

Balance the equation. –Law of conservation of mass –The mass of substances remains constant in chemical reactions. Mass of products ≡ Mass of reactants

Balance the equation. –Apply the Law of Conservation of Mass to get the same number of atoms of every element on each side of the equation. –Once one element is balanced, proceed to balance another, and another, until all elements are balanced. –Balance chemical formulas by placing coefficients in front of them. Do not add subscripts, because this will change the formulas.

Balance the equation Tip: Go to the most complex molecule first Tip: Start by balancing an element that appears in only one reactant and product. Don’t forget to put the state symbols in s, l, g, aq.

b) Mg + O 2  MgO Mg =1Mg= 1 O = 2 O = 1 Balance these skeleton equations: 2 2

NaOH + H 2 SO 4  Na 2 SO 4 + H 2 O Balancing equations:

NaOH + H 2 SO 4  Na 2 SO 4 + H 2 O Balancing equations: Step 1 Quick view see if you can see what missing / imbalanced

NaOH + H 2 SO 4  Na 2 SO 4 + H 2 O Balancing equations: Step2 Draw a box around each formula

NaOH + H 2 SO 4  Na 2 SO 4 + H 2 O Na = O = O = H = H = S = S= Balancing equations: Step3 Perform an inventory list

NaOH + H 2 SO 4  Na 2 SO 4 + H 2 O Na = 1 Na = 2 O = 5 O = 5 H = 3 H = 2 S = 1 S= 1 Balancing equations:

NaOH + H 2 SO 4  Na 2 SO 4 + H 2 O Na = 1 Na = 2 O = 5 O = 5 H = 3 H = 2 S = 1 S= 1 Balancing equations:

NaOH + H 2 SO 4  Na 2 SO 4 + H 2 O Na = 1 Na = 2 O = 5 O = 5 H = 3 H = 2 S = 1 S= 1 Balancing equations: Step 4 Place whole coefficients in front of boxes to achieve a balance. Focus on one element at a time but record all the changes

NaOH + H 2 SO 4  Na 2 SO 4 + H 2 O Na = 2 O = 6 O = 5 H = 4 H = 2 S = 1 S= 1 Balancing equations: 2

NaOH + H 2 SO 4  Na 2 SO 4 + H 2 O Na = 2 O = 6 O = 5 H = 4 H = 2 S = 1 S= 1 Balancing equations:

NaOH + H 2 SO 4  Na 2 SO 4 + H 2 O Na = 2 O = 6 O = 6 H = 4 H = 4 S = 1 S= 1 Balancing equations: 2 2

a) H 2 + O 2  H 2 O

H = 2 H = 2 O = 2 O = 1 Balance these skeleton equations: 2 2

A) K + B 2 O 3  K 2 O + B B) C + S 8  CS 2 We Do:

b) K + B 2 O 3  K 2 O + B Paired work: