Colligative Properties of Solutions Reaction Rates… How can I make a reaction happen faster?

What is a colligative property? A property that depends on: the concentration of solute particles in solution the solvent used A colligative property does not depend on: 1. the identity of the solute

Dilute Versus Concentrated Solutions Dilute--> a low amount of solute is dissolved in a solvent Concentrated--> a high amount of solute is dissolved in a solvent These terms will not tell us whether a solution is saturated, unsaturated, or supersaturated The concentration of a solution can be found using the Molarity (M) and Molality (m) equations

Freezing Point Depression When a solute is dissolved in a solvent, the freezing point of the solvent will depress (become lower) than the normal freezing point of the pure solute

What does the FP depression depend on? The amount the FP will be lowered depends on 3 factors: The concentration of the solution Higher molality (m) = higher depression Whether or not the solution is an electrolyte Electrolytes = higher depression The identity of the solvent used H2O vs. C2H5OH will exhibit different depressions

Practical Application of FP Depression Why does putting salt on the roads when it is icy prevent the roads from being slick? The addition of salt as a solute will lower the FP of H2O and help to prevent ice from forming

What Factors Affect the Rate of a Reaction? 1. Increase in surface area Ex. Increasing the surface area of a substance allows for more particle contact and collisions, therefore increasing the rate of a reaction Granulated sugar should dissolve more quickly in a solvent because of its greater surface area

2. Increase in temperature Ex. Increasing the temperature of a reaction allows for more frequent particle contact and collisions due to an increase in the kinetic energy of the system, therefore increasing the rate of a reaction

3. Increase in concentration of reactants Ex. Increasing the concentration of reactants allows for more particle collisions because there are more particles present, therefore increasing the rate of a reaction

4. Addition of a catalyst Ex. The addition of a catalyst will force the particles to come in contact at a quicker rate, therefore increasing the rate of the reaction • 5. Agitation/Stirring

The Collision Theory In order for a reaction to occur, 2 particles must have an effective collision. A successful collision needs: 1. Proper orientation (particles must hit in the right spots) 2. Suitable kinetic energy (particles must hit with the right amount of speed --> too much or too little may result in an ineffective collision)

Reaction Rate Diagrams Activation Energy (Ea) = the energy needed to get a reaction started This diagram is representing an exothermic reaction because energy is being released and the products contain less energy than the reactants Lowers Ea

Inhibitors increase Ea by slowing down a reaction