Reaction rates and equilibrium Flashcards
(29 cards)
what two conditions must occur for an effective collision.
- particles must collide with the correct orientation.
- The particles must have sufficient energy to overcome the activation of the reaction.
What four factors change the rate of chemical reaction.
- Concentration (pressure in gasses)
- Temperature
- Use of a catalyst
- Surface area of solid reactants.
Why does concentration or pressure of gas affect the rate of reaction?
When the concentration or pressure for gasses increases, the number of particles increases for the same volume, the particles are closer together and collide more frequently, resulting in more succesful collisions per unit time, increasing the rate of reaction.
What can the rate of reaction be defined as?
The change in concentration of a reactant or product over time.
what graph is rate of reaction the gradient of?
Concentration time graph.
What does a catalyst do?
Increases the rate of a chemical reaction without being used up in the overall equation. The catalyst increases the rate of reaction by providing an alternative pathway with a lower activation energy.
What is the difference between homogeneous and heterogeneous catalysts?
Homogeneous catalysts are the same physical state as the reactants. A heterogeneous catalyst has a different physical state as the reactants.
How does a homogeneous catalyst work?
The catalysts reacts with the reactants to form an intermediate compound, which then breaks down to reproduce the catalyst and produce the products.
How does a heterogeneous catalyst work?
Heterogeneous catalysts are usually solids, their reactant a (usually gas or aqueous solution) are absorbed into the surface of the catalyst, react to produce the product and catalyst then the product deabsorbs out of the catalyst.
What is the economic and sustainable impacts of catalysts?
Catalysts reduce the activation energy needed for a reaction, this inturn requires less energy for the react to occur, leading to less electricity use.
- leading to less fossil fuels being burnt to produce the electricity.
- Leading to larger profits as less is spent on electricity.
Why might a catalyst not be beneficial for the enviroment?
The catalyst could be toxic and prove worse for the enviroment.
What two methods are used to measure rate of reaction?
- Loss of mass by mass balance.
- Volume of gass produced using gass collection.
-Both should be measured over a period of time
Why can mass loss and volume gain be used to measure rate of reaction?
Both volume of gass produced and mass lost are proportional to rate of reaction.
What does the Boltzman distribution show?
The distribution of molecular energies in gases.
What are the features of the Boltzman distribution?
- No molecules have zero energy (Curve starts at the origin)
- The area under the graph is equal to the total number of molecules.
- There is no maxiumum energy for a molecule, the curve never touches the x axis after the origin / at high energy.
What does the temperature do to the boltzman distribution?
Lowers and shifts the peak to the right.
What does increasing the tempertaure do to the rate of reaction?
Leads to a higher rate of reaction.
More molecules have a greater or equal amount of energy to the activation energy, leading to more succesful collisions and a higher rate of reaction
What does adding a catalyst do to the rate of reaction?
Lowers the activation energy so a larger proportion of molecules can succesfuly react leading to a high rate of reaction.
Define dynamic equilibrium
The rate of forward raction is equal to that of the rate of reverse reaction. The concentration of the reactants and products saty the same.
what does Le chatelier’s principle state?
when a system in equilibrium is subject to external change, the system adjusts to minimise said change.
what happends to the equilibrium constant if more products or reactants are formed?
- If more products are formed the equilibrium constant shifts to the right (products).
- If more reactants are formed the equilibrium constant shifts to the left (reactants).
For the equation
2CrO4 2- + 2H+ -> Cr2O7 2- + H2O
(yellow) (orange)
what happens if acid (H+) is added?
When acid is added the H+ ion concentration increases, the forward reactions increases to produce more product (Cr2O7 2- and H2O) to minimise the change the addition of H+ ions. The position of equilibrium therefore shifts to the right. A stronger orange colour is seen.
For the equation
2CrO4 2- + 2H+ -> Cr2O7 2- + H2O
(Yellow) (Orange)
what happens if base (OH-) is added?
When (OH-) ions are added the concentration of H+ ions decreases, the rate of the forward reaction decreases to increase the concentration of H+ ions to minimise the change. A new position of equilibrium is established, shifted to the left. Yellow colour should be seen more.
What happens to the position of equilibrium if an increase in temperature occurs and why?
The position of equilibrium shifts towards the endothermic side, to take in heat energy, minimising the change (increase in temp).
