reaction kinetics Flashcards
(32 cards)
What is the rate of a reaction?
The speed at which a chemical reaction takes place, with units mol dm-3 s-1.
How can the rate of reaction be calculated?
Rate of reaction = change in amount of reactants or products (mol dm-3) / time (s).
What is the formula to calculate moles from mass?
Moles = mass (g) / molar mass (g mol-1).
What is the relationship between concentration and reaction rate?
An increase in concentration causes an increased collision frequency and therefore an increased rate of reaction.
What does collision theory state?
For a chemical reaction to occur, particles must collide with the correct orientation and sufficient energy.
What is activation energy (Ea)?
The minimum energy that colliding particles must have for a collision to be successful.
Define effective and ineffective collisions.
Effective collision: correct orientation and sufficient energy. Ineffective collision: incorrect orientation or insufficient energy.
What effect does increasing pressure have on reaction rates involving gases?
Increased pressure leads to more effective collisions and increases the rate of reaction.
What happens to the concentration of reactants and products as a reaction proceeds?
The concentration of reactants decreases while the concentration of products increases.
How can the rate of reaction be calculated from a concentration-time graph?
By determining the slope of the tangent at a point on the curve.
What is the effect of temperature on reaction rates?
Increasing temperature raises kinetic energy, leading to more frequent and effective collisions.
What is the Boltzmann distribution curve?
A graph showing the distribution of energies among particles at a certain temperature.
What happens to the Boltzmann distribution curve when temperature increases?
The curve flattens and the peak shifts to the right, indicating more particles have energy above the activation energy.
What is a catalyst?
A substance that increases the rate of reaction without being consumed, by providing an alternative pathway with lower activation energy.
Differentiate between homogeneous and heterogeneous catalysts.
Homogeneous catalysts are in the same phase as reactants; heterogeneous catalysts are in a different phase.
Fill in the blank: The rate of reaction can be calculated as the change in _______ of reactants or products over time.
[amount]
True or False: The activation energy is higher in exothermic reactions than in endothermic reactions.
False.
What is the effect of a catalyst on activation energy?
It lowers the activation energy required for the reaction.
How does collision frequency relate to reaction rates?
Higher collision frequency increases the likelihood of effective collisions, thus increasing reaction rates.
What happens to the rate of reaction over time?
The rate generally decreases as reactants are consumed and their concentration decreases.
What is the relationship between concentration and rate of reaction as shown in a rate-concentration graph?
The rate is directly proportional to the concentration of reactants.
What is a homogeneous catalyst?
A catalyst that is in the same phase as the reactants
For example, all components being liquids.
What is a heterogeneous catalyst?
A catalyst that is in a different phase than the reactants
For example, reactants being gases and the catalyst being a solid.
How does a catalyst affect the activation energy of a reaction?
It allows the reaction to take place through a different mechanism with lower activation energy.
