Chemistry - Ch. 18.1 and 18.3 Flashcards
rate
a measure of how much something changes within a specified amount of time
how is the rate of a chemical reaction (reaction rate) expressed?
change in amount of reactant or product per unit of time
What is the collision theory used for?
to relate the properties of particles to the rates of chemical reactions
Collision Theory
what happens if they don’t have an effective collision?
particles can react to form products when they collide if the particles have enough kinetic energy
- an ineffective collision will result in the particles bouncing apart, unchanged.
Activation Energy
the minimum energy that colliding particles must have in order to react
Activated Complex
an unstable arrangement of atoms that forms for a moment at the peak of the activation-energy barrier
What is the lifetime of an activated complex?
When does it’s existence end?
What is it sometimes called?
(3)
10^(-13) seconds
It’s existence ends with the reformation of the reactants or the formation of products
The transition state
Endothermic
Exothermic
absorbs heat
releases heat
Factors that determine whether a molecular collision results in a reaction? (4)
Temperature
Concentration
Particle Size
Use of a catalyst
What effect does the temperature of a solid, liquid, or gas have on the rate of reaction?
Increase Temp = Speeds up reaction, particles move faster
Decrease Temp = Slows down reaction, particles move slower
What effect does the concentration of a solid, liquid, or gas have on the rate of reaction?
Increase Concentration = Faster reaction rate, increases frequency of collision
What effect does the particle size of a solid, liquid, or gas have on the rate of reaction?
Increase particle size = Slower reaction rate, smaller surface area, and a decrease in frequency of collisions
Decrease particle size = faster reaction rate, greater surface area, increase in frequency of collisions
What are two other ways to increase the surface area of a solid?
Dissolve them
Grind into a fine powder
What is the best way to increase the rate of reaction?
Use a catalyst
Catalyst
a substance that increases the rate of reaction without being used up during the reaction
What are enzymes?
the catalysts that increases the rates of biological reactions
inhibitor
what does it do?
what happens to the reaction?
substance that interferes with the action of a catalyst
reduces the amount of catalyst available for a reaction
slows down or even stops.
reversible reaction
one in which the conversion of reactants to products and the conversion of products to reactants occur at the same time
equilibrium position
what does this tell you?
the relative concentrations of the reactants and products at equilibrium
it tells you whether the forward or reverse reaction is more likely to happen
Le Chatelier’s Principle
If a stress is applied to a system in dynamic equilibrium, the system changes in a way that relieves the stress
Stresses that upset the equilibrium of a chemical system? (3)
Changes in the concentration of reactants or products
Changes in temps
Changes in pressure (gases only)
effect of a change in concentration on a system at equilibrium?
Adding a product to a reaction at equilibrium pushes a reversible reaction in the direction of the reactants and vice-versa.
effect of a change in temperature on a system at equilibrium?
Increasing the temperature causes the equilibrium position of a reaction to shift in the direction that absorbs heat.
effect of a change in pressure on a system at equilibrium?
3
- Gases Only
- only occurs if there is an unequal number of moles of gas on each side of the equation - the side that has the least amount of moles is where the direction will shift towards
