CHAPTER 10: REACTION RATES AND EQUILIBRIUM Flashcards
What is meant by rate of reaction?
The rate of a reaction measures how fast a reactant is being used up or how fast a product is being formed.
What factors change the rate of a chemical reaction?
Concentration (or pressure), temperature, use of a catalyst or larger surface area.
What is the collision theory?
Two reacting particles must collide for a reaction to occur. In most collisions, the molecules collide but bounce off of each other and remain unchanged. Only a small proportion of collisions result in a chemical reaction.
Why are some collisions ineffective?
For a collision to be effective, two conditions have to be met. The particles must collide with the correct orientation, and the particles must have sufficient energy to overcome the activation energy barrier of the reaction.
How does increasing the concentration affect the rate of reaction?
An increase in concentration increases the number of particles in the same volume. The particles are closer together and collide more frequently. In a given period of time there will therefore be more effective collisions (correct orientation and sufficient energy) and an increased rate of reaction.
How does increasing the pressure of a gas affect the rate of reaction?
The concentration of the gas molecules increases as the same number of gas molecules occupy a smaller volume. The gas molecules are closer together and collide more frequently, leading to more effective collisions in the same time.
What are methods for following the progress of a reaction?
Monitoring the removal (decrease in mass) of a reactant, following the formation (increase in mass) of a product.
In a reaction that produces gas, how can you determine the rate of a reaction?
Monitoring the volume of gas produced at regular time intervals using a gas collection, or monitoring the loss of reactants using a balance.
How can a rate of reaction be calculated?
rate = change in concentration or mass / time
What does a catalyst do?
A catalyst increases the rate of a chemical reaction by providing an alternative reaction pathway of lower activation energy. It is not used up in the reaction, but may react with a reactant to form an intermediate or surface where the reaction can take place. At the end of the reaction, is is regenerated.
What is a homogeneous catalyst?
A homogeneous catalyst has the same physical state as the reactants. The catalyst reacts with the reactants to form an intermediate. The intermediate then breaks down to give the product and regenerates the catalyst.
What is a heterogenous catalyst?
A heterogeneous catalyst has a different physical state from the reactants. Heterogeneous catalysts are usually solids in contact with gaseous reactants or reactants in solution. Reactant molecules are adsorbed (weakly bonded) onto the surface of the catalyst, where
the reaction takes place. After reaction, the product molecules leave the surface of the catalyst by desorption.
What is the sustainability and economic importance of catalysts?
It a chemical process requires less energy, then less electricity or fossil fuel is used. Making the product faster and using less energy can cut costs and increase profitability. The modern focus on sustainability requires industry to operate processes with high atom economies and fewer pollutants. Using less fossil fuel will cut emissions of carbon dioxide, a gas linked to global warming.
What are the features of a Boltzmann distribution?
- No molecules have zero energy - the curve starts at the origin.
- The area under the curve is equal to the total number of molecules.
- There is no maximum energy for a molecule - the curve does not meet the x-axis at high energy.
How does higher temperature affect the Boltzmann distribution?
More molecules have an energy greater than or equal to the activation energy. Therefore a greater proportion of collisions will lead to a reaction, increasing the rate of reaction. Collisions will also be more frequent as the molecules are moving faster, but the increased energy of the molecules is much more important than the increased frequency of collisions.
