Chemical Reactions

Goal of the class To be able to identify and balance reactions Question of the day: Why do reactions have to be balanced? Previous Answer: Polar molecules attract each other with their electromagnetic charge. Previous question: How do polar molecules interact with each other?

→ Reactions Reactions occur when bonds are broken or formed. Every kind of bond will have some chemical energy. Reactions are observable with large enough quantities of compounds Always result in a chemical change →

Reactions Signs Many reactions can seen without any equipment Signs of reactions Change in colour Production of gas Change in temperature Change in odour Giving off heat, light, or energy Formation of a precipitate

Chemical Equations Chemical equations are used to show the results of a reaction The parts that go into the reaction are the reactants The end results are the products The state is shown in brackets after each chemical (s) = solid, (l) = liquid, (g) = gas, (aq) = aqueous dissolved in water -- aq Photosynthesis: CO2 (g)+ H2O (l) + sunlight → C6H12O6 (s) + O2 (g)

Reactions and Matter All reactions must follow the law of conservation of mass The number of atoms must be the same on both sides Amounts of atoms are written with coefficients. Photosynthesis: 6 CO2 (g)+ 6 H2O (l) + sunlight → C6H12O6 (s) + 6 O2 (g) Carbon + Water → Glucose + Oxygen dioxide

Balancing Reactions Balanced equations must contain all reactants and products Example: If you have react 1 mole of O2 with 3 moles of H2, you will have 2 mole of H2O and 1 mole of H2 3H2 + O2 → 2H2O + H2

Practice Balanced the following reactions: Fe + Cl2 → FeCl3 Fe + O2    →    Fe2O3 Na + H2O →    NaOH + H2. 2Na + 2H2O    →    2NaOH + H2.

Reaction Energies All reactions require energy in order to occur During a reaction, energy may be released or absorbed by the reaction Energy can be released in different ways Typically released or absorbed as heat Exothermic – Heat is given off Endothermic – Heat is absorbed. Give example of flame needed to light gas on stove.

Reaction Rates Not all chemical reactions are observable by inspection. Some require tests Some reactions occur very quickly (explosions, biochemical changes) Some chemical changes occur very slowly (rust, corrosion) Talk about water’s shape and how they will learn why it’s that way

Vocabulary Precipitate – to come out of a solution in solid form; a solid that exists outside of a solution Reactants – any of the atoms or molecules that take place in a chemical reaction Products – the remaining molecules after a chemical reaction impossible to solve.

Homework Pleases complete Chemical Interactions workbook pages 28-30 up to Q20. impossible to solve.