Lesson 7 Chemical Reactions and Reaction Rates

Core Content SC-HS Students will: identify variables that affect reaction rates; predict effects of changes in variables (concentration, temperature, properties of reactants, surface area and catalysts) based on evidence/data from chemical reactions. Rates of chemical reactions vary. Reaction rates depend on concentration, temperature and properties of reactants. Catalysts speed up chemical reactions. DOK 3

Lesson 7 When chemical bonds form or are broken, new substances are produced. This is the result of a chemical reaction: the process in which one or more substances change in a way that produces different substances. Chemical reactions occur at different rates.

Lesson 7 During a chemical reaction, one or more substances either bond together or break apart to form one or more new substances. Reactants: is the substances at the beginning of the reaction (left side of arrow). Products: is the substance(s) formed from the reaction (right side of the arrow).

Lesson 7 2 H O 2 → 2 H 2 O REACTANTSPRODUCTS

Lesson 7 There are four types of chemical reactions: Composition (Synthesis) Decomposition Single Replacement Double Replacement

Lesson 7 Composition (Synthesis) Reaction: when two or more substances come together to form a new substance. A + B → AB Sodium + Chlorine → Sodium Chloride 2 Na + 1 Cl 2 → 2 NaCl

When an element combines with oxygen they form what is called an oxide. Almost all metals react with oxygen to form oxides. Iron (s) + Oxygen (g) → Iron (II) oxide “rust” ___ Fe(s) + ___ O 2 (g) → ___ FeO(s) Balance the oxygen atoms first 1 O Fe O x 2 = Is everything now balanced, if so place a 1 in the rest of the blanks. x 2 = 2

When an element combines with sulfur they form what is called an sulfide. The metals in group one react with sulfur to form sulfides. Barium (s) + Sulfur (s) → Barium sulfide (s) ___ Ba(s) + ___ S 8 (s) → ___ BaS(s) Balance the sulfur atoms first 1 S Ba S x 8 = When you do this you must change the Barium as well. x 8 = 8 Balance Barium on other side now x 8 = 8 Is everything balance, place 1 in remaining blanks.

Lesson 7 Decomposition reaction: is one compound breaks down into simpler substances. AB → A + B Hydrochloric Acid → Hydrogen gas + Chlorine gas 2 HCl → 1 H Cl 2

Lesson 7 Single Replacement: when one substance replaces or switches places with another substance. A + BC → AC + B Hydrogen gas + Sodium chloride → Hydrochloric acid + Sodium metal 1 H NaCl → 2 HCl + 2 Na

Lesson 7 Double Replacement: when the substances in the reaction changes partners. AB + CD → AD + BC Iron chloride + Potassium sulfide → Potassium chloride + Iron sulfide 2 FeCl K 2 S → 1 Fe 2 S KCl

Lesson 7 Chemical reactions are affected by what is called reaction rates. Reaction rate: is the speed at which a chemical reaction takes place. The reaction rate is determined by measuring the change in concentration of a reactant or product per unit of time.

Lesson 7 There are several factors that affect the reaction rate. CauseEffectResult Increased temperature Faster speed of particles Increased # of collisions Faster rate of chemical rxn’s Increase pressure of gas More particles come in contact Increased # of collisions Faster rate of chemical rxn’s Increased concentration More particles available for contact Increased # of collisions Faster rate of chemical rxn’s Presence of a catalyst Catalyst acts to speed up rxn Makes it easier for particle to react Faster rate of chemical rxn’s

Lesson 7 Temperature: is a measure of the average kinetic energy of the molecules in a substance. Pressure: force exerted on the unit of area of surface. Concentration: amount of molecules present in a unit volume. Catalyst: an agent that speeds the rate of chemical reaction without being permanently changed or used up.

Lesson 7 Reaction Rate → Pressure & Concentration Temperature → As the pressure, concentration, and temperature rates increase then the reaction rate rapidly occurs.

Lesson 7 - Assignment 1. What can cause a chemical reaction to increase? (list all of them) 2. As the number of collisions between reactants increases, the rate of reaction ___. 3. An increase in temperature speeds the reaction rate because the distance between molecules ____.

Lesson 7 Video Clips Chemical Reactions