Chemical Reactions & Equations

Goals Observe Physical Changes associated with a Chemical Reaction Give evidence of the occurrence of a chemical reaction Write a balanced equation for a chemical reaction Identify the type of reaction

How do we know when a reaction occurs? Bubbles/fizzing (liquid  gas) Precipitation (solution goes cloudy and you see a ‘rain’ of solid particles falling to the bottom of the test tube) A change in the color of the mixture The solution gets hotter or colder Disappearance of a solid You see light given off

Balancing a Chemical Reaction In a reaction there are reactants (what we start with) products (what we end up with) In a chemical equation we write reactants  products A chemical equation needs to be balanced so that the same number of each type of atom are present on both sides To balance a reaction we write a number called a coefficient in front of the chemical formula for a reactant or product

Balancing a Chemical Reaction Nitrogen gas and Hydrogen gas react to make Ammonia N 2 (g) + H 2 (g)  NH 3 (g)(unbalanced reaction) There are 2 N on the left But only 1 N on the right So we put a 2 in front of the NH 3 N 2 (g) + H 2 (g)  2NH 3 (g)(the 2 balances the N atoms) But what about the H? (there are 2 on the left and 6=2x3 on the right) N 2 (g) + 3H 2 (g)  2NH 3 (g)(the 3 balances the H atoms)

Types of Reaction Type of ReactionDescriptionExample Equation CombinationElements or compounds combine to make a more complex product Cu + S  CuS DecompositionA reactant falls apart into simpler fragmentsCaCO 3  CaO + CO 2 Single ReplacementOne element takes the place of another element in a compound Mg + 2HCl  MgCl 2 + H 2 Double ReplacementElements in two compounds swap placesAgNO 3 + NaCl  NaNO 3 + AgCl CombustionReactant and oxygen form oxidesS + O 2  SO 2

A. Magnesium and Oxygen Burn a 2-3 cm strip of Magnesium ribbon in a bunsen Use tongs to hold the Magnesium in the flame and wear goggles Write down your observations of the reaction and products Balance the reaction ____Mg(s) + _____O 2 (g)  _____ MgO(s) What type of reaction is this?

B. Zinc and Copper (II) Sulfate Pour 3 mL of Copper (II) sulfate into 2 identical test tubes Place a small piece of Zinc in one of the test tubes Observe the color changes Initially After 15 mins After 30 mins Balance the Equation ____Zn(s) + ____CuSO 4 (aq)  ____Cu(s) + ____ZnSO 4 (aq) What type of reaction is this?

C. Metals and Hydrochloric Acid (HCl) 3 test tubes each with 3 mL of 1M HCl To one add Copper (Cu) To one add Zinc (Zn) To one add Magnesium (Mg) Observe the reactions Any evidence of H 2 (g)? Bubbles? Can you explode the gas? Does the metal dissolve? Balance the reactions ___Cu(s) + ___HCl(aq) -  ____ CuCl 2 (aq) + ___H 2 (g) ___Zn(s) + ___HCl(aq) -  ____ ZnCl 2 (aq) + ___H 2 (g) ___Mg(s) + ___HCl(aq) -  ____ MgCl 2 (aq) + ___H 2 (g) What types of reactions are these?

D. Reactions of Ionic Compounds Reactant 1 Reactant 2 ObservationsBalance CaCl 2 Na 3 PO 4 ___CaCl 2 (aq) + ____Na 3 PO 4  ___NaCl(aq) + ___Ca 3 (PO 4 ) 2 (s) BaCl 2 Na 2 SO 4 ___BaCl 2 (aq) + ____Na 2 SO 4  ___NaCl(aq) + ___BaSO 4 (s) FeCl 3 KSCN___FeCl 3 (aq) + ____KSCN  ___KCl(aq) + ___Fe(SCN) 3 (s) React 20 drops and reactant 1 (in one test tube) with 20 drops of reactant 2 (in a second test tube) Describe them before they are mixed Describe them once they are mixed together Balance the reactions What type of reactions are these?

E. Sodium Carbonate (Na 2 CO 3 ) with HCl You are wearing goggles right? 3 mL of 1M HCl in a test tube Add a small amount of Na 2 CO 3 (sodium carbonate) Record observations (gasses?) Place a lit match or wood splint into the neck of the test tube what happens to the flame? Balance the reaction Na 2 CO 3 (s) + ___ HCl(aq)  ___ CO 2 (g) + ___ H 2 O(l) + ___NaCl(aq) What type of reaction is this?