Reaction Rates
What is the relationship between reaction rate and activation energy?
The higher the activation energy, the slower the reaction.
The lower the activation energy, the faster the reaction.
Catalysts lower the activation energy
Define dynamic equilibrium
If a reaction is in equilibrium, what happens if the concentration of products is doubled?
The reaction will shift to the left to favor formation of the reactants
What is the effect of temperature on reaction rate?
How does adding reactant (increasing concentration) affect the reaction rate?
Increasing the concentration of the reactant increases reaction rate by allowing for increased molecular collisions
Define homogenous and heterogenous catalysts
Homogenous catalysts are catalysts in the SAME phase as the reactants.
Heterogeneous catalysts are catalysts in a DIFFERENT phase than the reactants.
Given the following reaction:
N2(g) + 3H2(g) <----> 2NH3(g)
Write the equilibrium constant expression (Keq)
Keq = [NH3]2/[N2][H2]3
Given the following reaction at equilibrium:
H2 + I2 + 2.7kJ <---> 2HI
What would happen to the amount of 2HI when the temperature of the system is increased?
Increased temperature would shift the reaction to the right in favor of product formation, so the amount of 2HI would increase
If ∆G is positive, is the reaction exergonic or endergonic?
Endergonic
In a spontaneous reaction, will the products have more or less energy than the reactants? Is ∆G positive or negative?
The products will have LESS energy than the reactants, and ∆G will be NEGATIVE
Between homogenous and heterogenous catalysts, which is more commonly used in industry and why?
Heterogenous catalysts are more commonly used in industry because they are more easily separated from the reactants
The following lists different states of matter. Identify which states are used in writing an equilibrium constant expression (Keq) and which are not:
Solids (s)
Liquids (l)
Gases (g)
Aqueous substances (aq)
Solids and liquids are NOT included in the equilibrium constant expression
Gases and aqueous substances ARE included in the equilibrium constant expression
Given the following reaction:
HCl (aq) <---> H+ (aq) + Cl-(aq)
What would happen if a large amount of sodium chloride (NaCl) was added to the solution?
The equilibrium would shift to the left, favoring the formation of the reactant HCl.
How does pressure affect reaction rate?
Increasing pressure increases reaction rate IF the reactants contain more moles of gas than the products
Define collision theory
Particles must collide in order to react
Define enzymes. How is enzymatic activity regulated by the body?
Enzymes are biological catalysts (often proteins) that regulate cellular functions. The body uses feedback mechanisms to control enzyme activity.
Given the following reaction:
NH4NO3(s) <---> N2O(g) + 2H2O(l)
Write the equilibrium constant expression (Keq)
Keq = [N2O]
Given the following reaction at equilibrium:
2H2(g) + O2 (g) <---> 2H2O (g)
What would be the effect of increasing the pressure of the system?
Increasing the pressure shifts the equilibrium toward fewer molecules. In this case, there are 3 molecules of reactant (2H2 + 1 O2) and 2 molecules of product (2H2O). So increasing the pressure would shift the equilibrium to the right favoring more product formation.
Define activation energy
What are the two conditions needed for an effective collision between molecules?
Collisions must be energetic/have proper energy (1) and correct orientation (2)
Name one way that catalysts can increase reaction rate
Possible answers:
1) Hold reactant molecules in proper orientation to react
2) Provide alternative reaction pathway (form temporary reaction intermediates)
3) Weaken or break reactant bonds
Given the following reaction:
CO2(g) + 2H2(g) <---> CH3OH(g)
What is the value of the equilibrium constant (Keq) if the following concentrations are measured at equilibrium?
[CO2] = 0.50 M
[H2] = 0.25 M
[CH3OH] = 0.050
The value of Keq = [CH3OH]/[CO2][H2]2 = 1.6
1) Q < K
2) Q = K
3) Q > K
2) If Q=K, the reaction is at equilibrium; no shift will occur.
3) If Q>K, there is an overabundance of products. The system will shift towards the reactants.
Give a real-life example of the use of a catalyst
Lots of potential here:
- Catalytic converters in cars
- Specific enzymes in blood