Reaction Rate Chemistry

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Reaction Rate

time it takes for the reactant to become the product; no chemical reaction is instantaneous

For minimum energy required for chemical reaction to occur:

must separate (work is done);
particles are broken down by dipolar water molecules;
ions must fight throught the water to re-combine

3 ways used to study reaction rate:

(1) Measure the time it takes for the product to first appear;(colorless to a color)
(2) Measure the time it takes for one or both reactants to be used up (will change from one color to a new color);
(3) Measure the amount of product formed in a given length of time (need a measurable product such as gas or a solid).

K1 - K2S2O8 reaction (the iodine clock) reaction

was used to measure the time it takes for the product to first appear

KMnO4 - H2C2O4 reaction

was used to measure the time it take for one or both reactants to be used up

Shell - HCl reaction

was used to measure the amount of product formed in a given length of time

When potassium permanganate KMnO4 and oxalic acid H2C2O4 have reacted

the mixture turns from purple to golden yellow

When potassium iodine KI and potassium persulfate K2S2O8 have reacted

the solution turns from colorless to a dark blue to blue-black. YOu need to add starch (an indicator) to the mixture.

According to the particle model of mater

increasing the concentration of a reactant increases the number of particles available for collision.

More collision

means a faster reaction rate.

Concentration

is the amont of of solute, matter dissolved, in a given volume of solution.

Increasing concentration

has no effect on the speed of the matter particles, just the number of particles in a given volume of solution.

3 Methods for changing reaction rates

(1) Changing the concentration
(2) Changing the temperature
(3) Using a catalyst

Collision Theory

In order for a reaction to occur, particles must collide at the proper angle as well as have propery energy (force of collusion). Energy is neither created nor destroyed --->just changes form.

Temperature

is the measure of the motion of matter particles

KMnO4 - H2O2O4 turned from purple to golden yellow faster

faster when heated than when at room temperature

Kl - K2S2O8 turned from colorless to dark blue to blue-black

in less time when heated than at room temperature

Shell - HCl reaction was tested with 4 different temperatures

when the HCl was heated, the temperature increased, the amount of gas produced increased

When data from the temperature vs amount of product experiment was graphed

the relatioship shown was unlimited growth

The Particle Model of Matter, increasing temperature

increases the motion of matter particles, as the motion increases, the number of particle collisions increase, more particle collisions occuring, the reaction rate is faster.

Catalyst

is a substance that increases the reaction rate without itself being changed.

Experiment where a catalyst was added to hydrogen peroxide

when the reaction took place, a transition state took place, solution turned a temporary green color. After reaction was complete, the solution turned back to the original red color of the colbalt.

Reaction rate of KMnO4 - H2C2O4 increased

when a drop of manganous sulfate MnSO4 was added. The MnSO4 did not react to the KMnO4, the MnSO4 was not a reactant

Reaction rate of Kl - K2S2O8 was increased

when a copper BB was added. Copper BB did not react the K1, Cooper BB was not a reactant in this reaction

MnSO4

had no reaction on the K1 - K2S2O8 reaction rate

3 Characteristics of Catalyst

(1) used in small amounts, only a drop of one BB was used;
(2) Catalysts are not reactants
(3) Catalysts are specific for a few reactants. (MnSO4 works for KMnO4 - H2C2O4 reaction but not K1 - K2S2O8 reaction)

Additional Characteristics of Catalyst

(1) catalyst may be used for more than one reaction; (BB works well here)
(2) Catalysts are found in living or once living matter;
(3) Catalysts such as the apple or potatoe (called enzymes) since bubbles formed on its surface.

Enzymes

Catalysts found in living and once living matter

Characteristics of Enzymes

made by living things
end in -ase
sensitive to heat
can be regulated
living things can literally turn a catalyst on/off

Activation energy

minimum energy required for a reaction to occur

Decomposition reaction rate

when a compound heats up the atoms break apart and separate.

Exothermic reaction

energy is released during the reaction, a net temperature change will increase. It takes more energy for the particles to separate than they release when they re-combine.

Endothermic reactions

energy that is absorbed during the reaction. Gets colder and if the energy involved is heated, the products woudl appear colder than the reactants.

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