Rate of reactions – can be fast- explosions – can be slow- rusting – as a reaction takes place concentration of reactants decreases (negative) over time concentration of products increase (positive) over time – normally measure in Molarity per sec (M/s) – will continue until reaches equilibrium or one of the reactants is used up
Measuring rate of reactions – can measure: mass or volume change for gaseous reactions – mass would go down as gas escapes – volume would increase at constant temp. and pressure – pressure would increase at constant temp. and volume change in pH if acids and bases are involved change in electrical conductivity – if produces ions in solution, conductivity will increase using a spectrometer to detect color changes
usually involves a graph of properties over time usually a curve, and the reaction rate is determined from the slope of the line at a time (also known as a tangent) reaction rates tend to slow with time as reactants are converted to products Determining Rate of Reaction from reactions (C ONCENTRATION, V OLUME, and M ASS )
reaction slows down with time because the C ONCENTRATION of the reactants decreases “rise over run” –.040M/200s =.0002M/s –.025M/400s =.000063M/s Example C 4 H 9 Cl(aq) + H 2 O(l) C 4 H 9 OH(aq) + HCl(aq)
Activation Energy E a. a minimum amount of energy required for reaction to occur –bonds need to be broken first the molecules must posses sufficient energy to get over the activation energy barrier.
Collision theory (Topic 6.2) in order for particles to react – particles must collide – must collide in the correct orientation/angle – must collide with enough kinetic energy to overcome the activation energy (E a ) if the previous conditions are “enough”, particles can overcome the activation energy and reaction will occur – meaning the bonds holding the reactants together will be broken
Factors That Affect Reaction Rate s any factor that increases the frequency of collisions or increases the energy with which particles collide will make the reaction go faster: 1.temperature 2.pressure 3.surface area 4.concentration 5.catalysts
1. Temperature increase temp – increases number of collision per unit time reaction rate approximately doubles for each 10 o C or K rise in temperature – increases energy of the collisions
2. Pressure only for gasses – reducing volume while keeping temp constant forcing them together will increase number of collisions
3. Surface area smaller particles have more surface area – only the particles on the surface can come in contact with a reactant – more collisions per unit time
Maxwell–Boltzman energy distribution curve another way to look at what particles can react area under the curve shows the number of gas particles not all gas particles have the same energy – only some gas particles (blue area) have enough energy to react
the area under the curve remains the same because the number of particles doesn't change higher temps. shifts the curve to the right (therefore, the peek must be lower) resulting in an increase in collision frequency and thus more successful collisions
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