Collision Theory
What two things must happen in a collision for a reaction to occur?
Have enough energy (≥ activation energy) and the correct orientation.
How does increasing concentration usually affect reaction rate?
Rate usually increases because there are more collisions.
Is heat released or absorbed in an exothermic reaction?
Exothermic: heat is released; ΔH is negative.
State Le Chatelier’s Principle in one short sentence.
A system at equilibrium shifts to counter a change.
What ion does an acid produce in water?
H+
How does raising the temperature affect particle speed?
Particles move faster.
Why does breaking a solid into smaller pieces speed up its reaction?
More surface area means more places for collisions to happen.
On an energy diagram, which is higher: reactants or products for an endothermic reaction?
For endothermic, products are higher in energy than reactants.
If you add more product to a system at equilibrium, which way does the reaction shift?
It shifts toward reactants (to use up the added product)
What ion does a base produce in water?
OH-
What is activation energy in simple terms?
The energy barrier particles must overcome to react.
How does decreasing the volume of the container affect the rate of a gas reaction?
Lower volume → higher pressure raises gas concentration → more collisions → faster rate.
What is the activation energy shown as on a potential energy diagram?
The reactants to the top of the hill; distance from reactants to top of the hill.
For N2(g) + 3H2(g) ⇌ 2 NH3(g), what happens to equilibrium if volume is decreased?
Decreasing volume increases pressure → shifts right to produce more NH3 → toward side with fewer gas moles.
Give the conjugate acid of NH3.
NH4+
What role does particle orientation play in reactions?
If particles are not oriented correctly, they may not react even if they collide.
Name the four ways to make a reaction go faster.
Increase temperature, increase concentration, add a catalyst, increase surface area.
If a reaction releases 80 kJ, is ΔH positive or negative?
ΔH is negative (−80 kJ)
If temperature is increased for an exothermic reaction, which direction does equilibrium shift?
Shifts toward reactants (left) to absorb added heat since heat is on the product side.
If [H+] = 0.01 M, what is the pH?
pH = 2 (since 0.01 = 1 x 10-2)
(pH = −log[H+] = −log(0.01))
What is another term for average kinetic energy?
Temperature
If you double the concentration of a reactant in a reaction that is first order, what happens to the rate?
The rate doubles.
Does a catalyst change how much heat a reaction gives off or absorbs? (Yes/No & EXPLAIN WHY)
No — catalysts do not change ΔH because the distance between reactants and products stays the same.
For 2 NH3(g) ⇌ N2(g) + 3 H2(g), name three ways to shift the reaction towards the reactants.
Add [H2], Add [N2], increase pressure, decrease volume of container
Given the following equation:
H2O (l) + H2O (l) ⇌ H3O+ (aq) + OH- (aq),
at equilibrium, water is neutral and [H3O+] & [OH-] is equal.
Using Le Chatelier's Principle, describe what happens if you add NaOH to neutral water.
[OH-] would increase, meaning [H3O+] would decrease because the NaOH is dissociating making the water more basic/alkaline.