Chemical Reactions

Physical Change Any change where the composition does NOT change. Can be reversible or irreversible PHASE CHANGES are in this category! Break, split, grind, cut, crush, tear, melting/boiling (points), etc.

Chemical Change The composition MUST change Burn, rot, rust, decompose, ferment, explode, and corrode Test before and after…

Reactant vs. Product Reactant: Present before reaction Product: Produced in a reaction The arrow is read “gives, yields, or reacts to produce”

You Try… Label the reactant(s) and product(s) in the following reactions CH4 + O2  CO2 + H2O Hydrogen peroxide  water + oxygen AB + CD  AD + CB MgO  Mg + O2 Hydrochloric Acid + Magnesium  Magnesium Chloride + Hydrogen gas

Type 1 What do you think the Law of Conservation of Mass means? How might it relate to you, our class, or the environment? Fill at least 3 lines.

Zero A Scale

Law of Conservation of Mass Mass is not created nor destroyed

Did the Following Obey? Why or why not?

Coefficients vs. Subscripts Draw/write out the following: 2Cl 2Cl2 H2O vs. 3H2O H3PO4 vs. 2H3PO4 We can write a chemical equation and see if it obeys… 2Al + Fe2O3  Al2O3 + 3Fe

Are the following consistent with the Law of Conservation of Mass Are the following consistent with the Law of Conservation of Mass? Why or Why Not? CaCl2 + 2NaOH  Ca(OH)2 + NaCl 2Cu + 2HCl  H2 + CuCl2 2Zn(s) + O2(g)  2ZnO(s) C2H6 + 3O2  2CO2 + 3H2O 2NaOH + H2SO4  Na2SO4 + 2H2O MgO + 2HC2H3O2  H2O + Mg(C2H3O2)2 6CO2(g) + 3H2O  C6H12O6 + 2O2(g)

Combustion and Bond Energy Exothermic vs. Endothermic

Combustion and Bond Energy Compounds contain chemical bonds All chemical bonds contain different amounts of stored energy: C-C C-N 348kJ 293kJ Energy is required in order to break bonds Energy is given off when bonds are formed

Chemical Reactions AB + CD  AD + CB A-B + C-D  A-D + C-B Reactant bonds (A-B and C-D) must be broken Product bonds (A-D and C-B) must be formed

Do the math… Depending on the number and type of bonds broken and/or formed during chemical reactions, energy is either given off or required in chemical reactions CH4 + 2O2  CO2 + 2H2O + 890kJ

CH4(g) + 2Cl2(g) + 2F2(g)  CF2Cl2(g) + 2HF(g) + 2HCl(g) Calculations Each compound must be drawn out in order to see and label bond energies *Use given sheet* CH4(g) + 2Cl2(g) + 2F2(g)  CF2Cl2(g) + 2HF(g) + 2HCl(g) Bonds broken-bonds formed will give you the overall energy in a reaction! Reactants – Products

Exothermic vs. Endothermic Exothermic: In a chemical reaction energy is given off (kJ is on the product side, or is negative) Ex: CH4 + 2O2  CO2 + 2H2O + 890kJ Endothermic: In a chemical reaction, energy is required (kJ is on the reactant side, or is positive) Ex: N2 + O2 + 180.5 kJ  2NO This relates to bond energy

Environmental Chemistry?! The energy given off during certain chemical reactions can be captured and used (combustion reactions)! Beneficial to humans  CH4 + 2O2  CO2 + 2H2O