Rate Equations and Kp Flashcards
What is the reaction rate?
The reaction rate is the change in the amount of reactant or product per unit time. If the reactants are in solution, the rate will be the change in concentration per second.
How do you work out the gradient and therefore reaction rate from a curved graph?
You draw a tangent to the point in which you want to find out the gradient and then work it out from there.
What do the powers mean in the rate equation?
They are the orders of the reaction with respect to the reactant e.g A2 is order 2 with respect to A.
What is an order of reaction?
It is the power to which the concentration of its reactant is raised in the rate equation.
How do you find the overall order of a reaction?
You add the orders for each component up
How can you find the order of a reaction?
You can only find it through experimentation, you cannot find it from chemical equations.
What is k?
k is the rate constant, which is a number that links the rate of reaction to the concentration of the reactants. The bigger the value of k is, the faster the reaction.
Why does the rate constant increase as you increase temperature?
When you increase the temperature of a reaction, the rate of reaction increase, you are increasing the number of collisions between reactant molecules and also the energy of each collision. But the concentrations of the reactants and the order of the reaction stay the same. So the value of k must increase for the rate equation to balance.
How can the initial rates method be used to work out rate equations?
- repeat an experiment several times using different initial concentrations of the reactants, changing one at a time.
- calculate the initial rate for each experiment
- see how the initial concentrations affect the initial rates and figure out the order for each reactant.
How do you measure the rate of reaction via continuous monitoring?
You can follow a reaction all the way through to its end by recording the amount of product or reactant you have at regular time intervals. (continuous monitoring)
The results can be used to work out how the rate changes over time.
How would you measure rate of reaction using gas volume?
If a gas is given off you could collect it in a gas syringe and measure volume at regular time intervals. To find the concentration of a reactant at any time use the ideal gas equation and the molar ratio.
How would you measure rate of reaction using loss of mass?
If a gas is given off then the system will lose mass. You can measure this at regular intervals with a balance. Then use mole calculations to work out how much gas you have lost and therefore how many moles of reactants are left.
How would you measure rate of reaction using colour change?
Use a colorimeter
- plot a calibration curve using known concentrations
- during the experiment take a small sample from your reaction solution at regular intervals to read the absorbance
- use the curve to convert the absorbance to a concentration
What does a colorimeter do?
A colorimeter measures absorbance. The more concentrated the solution the higher the absorbance is.
How would you measure rate of reaction using a change in pH?
If the reaction produces or uses up H+ ions, the pH of the solution will change. So you could measure the pH of the solution at regular intervals and calculate the concentration of H+
What shape indicates zero order?
A straight line on a concentration time graph.
A horizontal line on a rate concentration graph
What shape indicates first order?
A curved line on a concentration time graph.
A straight line through the origin on a rate concentration graph.
What shape indicates second order?
A steeper curve on the concentration time graph.
A curve on the rate concentration graph.
What is the rate determining step?
Mechanisms can have one step or a series of steps. In a series of steps, each step can have a different rate. The overall rate is decided by the step with the slowest rate- the rate determining step.
How do orders or reaction provide information about the rate determining step?
All things included in the rate equation are part of the rate determining step. The order of a reaction with respect to a reactant shows the number of molecules of that reactant that are involved in the rate determining step.
What does the Arrhenius equation do?
The Arrhenius equation shows how the rate constant varies with temperature and activation energy.
k - rate constant
Ea - activation energy
T - temperature in K
R - gas constant
A - the Arrhenius constant
What is total pressure and what is partial pressure?
In a mixture of gases, each individual gas exerts its own pressure- this is called its partial pressure.
The total pressure of a gas mixture is the sum of all the partial pressures of the individual gases.
What is the equation for mole fraction of gas in a mixture?
number of moles of gas/total number of moles of gas in the mixture
What is the equation for partial pressure of a gas?
mole fraction of gas x total pressure of the mixture.
