Collision Theory • For chemical reaction to happen, their particles (atoms, molecules, or ions) must collide, and the collisions must result in interactions between species.
Chemical reactions aren’t for sissies! For any reaction to happen there must be a collision! I’m afraid of collisions! Don’t hurt me!
Collision Theory The “interaction” piece of collision theory is critical. If the molecules’ collision is too gentle, they just gently bounce off each other with no reaction.
Too gentle - no reaction! The particles rebound. Oops! So Sorry Pardon me!
Or if the orientation of the molecules is wrong (charges not aligned, ect.) There is no reaction. + - H H O
Collision Theory For two molecules to react, they must collide with enough energy to move valence electrons and disrupt the bonds of the molecules, and be correctly oriented.
Collision Theory Collision theory states that sufficiently strong collisions between molecules, in the correct orientation, must happen for reactions to occur.
Factors That Effect Reactions Again, a reaction between two molecules can only occur when a collision occurs between the two molecules. I’m ready for a chemical reaction! Let’s collide!
1. Temperature Raising the temperature increases the speed at which the molecules move. When molecules move faster, more collision occur, thus making the reaction proceed faster. The opposite is true for decreasing the temp.
2. Concentration When the concentration is increased, the number of molecules are increased. When there are more molecules, more collisions occur thus making the reaction proceed faster. The opposite is true for decreasing the concentration.
Too crowded! Increased concentration = more collisions, thus faster reaction
Decreased concentration = fewer collisions, thus slower reaction
3. Particle Size When the size of the particles are smaller the surface area is increased. This provides access to a greater number of molecuels and increases the speed of the reaction. The opposite is true for using larger particle sizes. Large particle, slow reaction Small particles, fast reaction
Surface area, From Large to Small Chunks or Lumps Large Pieces or granules Powder or dust Small
4. Catalysts Even though a catalyst is never used up in a reaction, their presence can speed up a reaction by lowering the energy it takes for collisions to occur.
Energy is part of Reactions Exothermic Reaction – when energy is released during a reaction it is called an exothermic reaction. This is observed as an increase in temperature. The words heat, light, or energy are written as a product.
Endothermic reaction – when energy is absorbed or taken in during a chemical reaction. This is observed as a decrease in temperature. The words heat, light, or energy are written as a reactant.
Don’t Forget… Chemical reactions must follow the Law of Conservation of Mass, which states that mass is neither created nor destroyed. The form of matter may change, but the TOTAL amount of mass stays constant. This law also means that the number of atoms must stay the same too!
Review! • According to Collision Theory, What needs to happen in order for a successful chemical reaction to occur? • Molecules need to collide with enough energy • Molecules need to collide in the correct orientation • Molecules need to collide slowly • Both A and B
Review! • Which choice would NOT increase the rate of a chemical reaction? • Increasing the concentration of molecules • Increasing the size of the particles • Adding a catalyst • Increasing the temperature
True/False • A catalyst is used to speed up chemical reactions • True • False
True/False • A catalyst is used up in a chemical reaction (meaning you can’t reuse it again!) • True • False
HCl FeCl3(s) + O2(g) Fe2O3(aq) + Cl2(g) • Which substance in the equation is a solid? • FeCl3 • O2 • Fe2O3 • Cl2 • HCl
HCl FeCl3(s) + O2(g) Fe2O3(aq) + Cl2(g) • Which substance in the equation is dissolved in water (aqueous)? • FeCl3 • O2 • Fe2O3 • Cl2 • HCl
HCl FeCl3(s) + O2(g) Fe2O3(aq) + Cl2(g) • Which substance in the equation represents a catalyst? • FeCl3 • O2 • Fe2O3 • Cl2 • HCl
Types of Chemical Reactions While there are literally thousands of different kinds of chemical reactions, most can be classified into 5 main types:
Synthesis (or addition or combination) • Decomposition • Single displacement (or single replacement • Double displacement (or double replacement) • Combustion
1. Synthesis Synthesis reactions occur when two or more reactants combine to form one new compound product. A + X AX 2Mg + O2 2 MgO
Real life please…. Rust is a synthesis reaction 4Fe + 3O2 Fe2O3
Many plastics are made with synthesis reactions…. Think of how often in a day you encounter plastic… think synthesis A + X AX
1. Synthesis Bella Edward Our romance starts when Bella moved to Oregon, and fell in love with Edward…
1. Synthesis = Bellward True Love…COMBINE together
2. Decomposition Occurs when one reactant decomposes to form two or more products. Decomposition is the opposite of synthesis. AX A + X 2HgO 2Hg + O2
2. Decomposition Rihanna&Chris Some couples are just not meant to be…
2. Decomposition = Rihanna + Chris …some couples SPLIT after a little “heat”
3. Single Displacement A lone element replaces an element with a similar charge in a compound. A + BC AC + B H2 + CuO H2O + Cu
Real life please… • Never store acids in metal containers because 2Al + 6HCl 2AlCl3 + 3H2 The metal container will dissolve, leaking the acid everywhere…
4. Double Displacement Occurs when positive and negative ions switch places. The old switch-a-roo! Make sure to match positive and negative ions together! AB + CD AD BC FeS + 2HCl FeCl2 + H2S
Real life please… 2HCl + Mg(OH)2 MgCl2 + 2H2O When your stomach is upset (heartburn, ect) and there is excess stomach acid, TUMS or milk of magnesia is used to neutralize the excess stomach acid.
4. Double Replacement Addison&McDreamy + Meredith&McSteamy Some couples are not satisfied with one another…and well…
4. Double Replacement = Addison&McSteamy + Meredith&McDreamy …couples SWITCH partners
5. Combustion Occurs when a hydrocarbon (a compound containing only hydrogen and carbon) burns by combining with oxygen. Carbon dioxide and water are the only products. Ex. C2H6 + 7O2 4CO2 + 6H2O
Hydrocarbons for combustion CH4 Methane - Natural gas C3H8 Propane – Gas grills C4H10 Butane - Lighters
Real Life Examples Complete combustion of methane: (burns with a blue flame – complete combustion very rare) CH4 + 2O2 CO2 + 2H2O
Incomplete combustion: Carbon doesn’t completely burn, some “ash” or “soot” left over. Flame burns with any color than blue.