rate equations Flashcards
What does the rate equation link together?
Rate with concentrations of substances
The equation often takes the form: Rate = K[A]^m[B]^n.
What is the definition of ‘order’ in a rate equation?
The power to which the concentration is raised in the rate equation
Orders indicate how concentration changes affect the rate.
What characterizes a zero order reaction?
Changes in concentration have no effect on the rate
Doubling the concentration does not change the rate.
What is the characteristic of a first order reaction?
Changes in concentration are proportional to changes in the rate
Doubling the concentration doubles the rate.
What defines a second order reaction?
Changes in concentration have a squared proportional change on the rate
Doubling the concentration results in a quadrupling of the rate.
What is the rate constant denoted by?
K
The rate constant links rate and concentration in the rate equation.
What is the temperature dependency of the rate constant?
The rate constant K is only fixed at a particular temperature
K increases with temperature, leading to a faster reaction rate.
How does an increase in temperature affect the rate of reaction?
It increases the value of K and the rate of reaction
Higher temperatures provide particles with more kinetic energy, resulting in more frequent collisions.
What is the significance of the rate constant K in the rate equation?
It allows the relationship between rate and concentration to be quantified
The units of K vary based on the overall order of the reaction.
What happens to the rate constant K when the temperature increases?
K increases
This results in a faster rate of reaction due to more effective collisions.
What is the relationship between concentration and rate in a second order reaction?
Rate changes are proportional to the square of the concentration
Example: Doubling concentration quadruples the rate.
What is an example of a zero order reaction?
A reaction where doubling the concentration does not change the rate
This indicates the concentration does not affect the reaction rate.
What does it mean if a substance has first order with respect to a reaction?
The rate changes proportionally with changes in concentration
If concentration is doubled, the rate also doubles.
How do you calculate the rate constant K?
K = Rate / [Concentration]^Order
Rearrange the rate equation to isolate K.
What are the steps to calculate the rate of reaction in a lab?
- Write the rate expression 2. Substitute known values 3. Calculate the rate
Ensure to account for the order of each reactant.
What is the expression for K in terms of rate and concentration?
K equals rate over the concentration of NO squared
K represents the rate constant in a rate equation
What are the units of K?
mole to the minus 1 dm cubed s to the minus 1
K’s units vary based on the reaction order and the specific reactants involved
How is the initial rate of a reaction defined?
The rate right at the start of the reaction
It is determined using the gradient of a tangent to the concentration vs. time graph at time zero
What method is used to determine the rate equation using initial rates?
Conducting experiments while changing the concentrations of reactants one at a time
This allows for the observation of how changes in concentration affect the rate
What is the order of a reactant if doubling its concentration results in quadrupling the rate?
Second order
This indicates a quadratic relationship between concentration and rate for that reactant
How do you determine the order with respect to a reactant?
Compare experiments where the concentration of that reactant changes while others remain constant
This isolates the effect of the reactant on the rate
What is the rate equation for the reaction of nitrogen monoxide with chlorine?
rate equals K concentration of NO and concentration of Cl
It is first order with respect to both NO and Cl
What should you do if no concentration remains constant in a set of experiments?
Add an extra column to show the theoretical rate if one reactant is kept constant
This allows for comparison to determine the effect of the varying reactant
What is the iodine clock reaction?
A reaction that changes color over a specific time period, involving hydrogen peroxide, iodide ions, and starch
It produces iodine, which reacts with starch to create a deep blue-black color
What role does sodium thiosulfate play in the iodine clock reaction?
It reacts immediately with iodine to prevent color change until it is consumed
Once sodium thiosulfate is depleted, iodine reacts with starch, indicating the end of the reaction
What is the initial rate calculated from the gradient of a tangent?
Change in Y over change in X
This represents the rate of reaction at the very beginning, measured in grams per minute or other units
Fill in the blank: The gradient at zero minutes is determined using the _______.
tangent to the curve
This reflects the instantaneous rate of reaction at the start
True or False: The rate constant K changes with temperature.
True
K is temperature-dependent, meaning its value can change if the temperature of the reaction is altered
What is the role of sodium thiosulfate in the iodine clock reaction?
Sodium thiosulfate reacts immediately with iodine produced in the reaction, preventing the blue-black color until all thiosulfate is consumed.
What indicates the end of the iodine clock reaction?
The appearance of a deep blue-black color due to iodine reacting with starch after all sodium thiosulfate has reacted.
How can the order of a reaction be determined using the iodine clock reaction?
By varying the concentration of iodine or hydrogen peroxide and measuring the time taken for the blue-black color to appear.
What is one method to monitor the rate of reaction using a disappearing cross?
Place a reaction vessel over a paper with a cross and time how long it takes for the cross to disappear.
What factors can affect the rate of a chemical reaction?
Concentration of reactants, temperature, presence of catalysts, and surface area.
How can pH changes be used to measure reaction rates?
By using a pH meter to measure pH at regular intervals and calculating the H+ ion concentration.
What is the method for measuring mass loss in a reaction?
Using a top pan balance to measure the mass of the reaction vessel before and after the reaction, suitable for gas-producing reactions.
What is the purpose of using a gas syringe in measuring reaction rates?
To trap and measure the volume of gas produced over time during a reaction.
How can color change be monitored in a reaction?
Using a colorimeter to measure the absorbance of light from a colored sample.
What is a calibration curve in the context of measuring absorbance?
A graph created by plotting known concentrations against their absorbance to determine unknown concentrations in a sample.
What does a zero-order reaction look like on a rate concentration graph?
A horizontal line indicating that changes in concentration do not affect the rate of reaction.
What does a first-order reaction look like on a rate concentration graph?
A straight diagonal line indicating that the rate of reaction changes proportionally with concentration.
What does a second-order reaction look like on a rate concentration graph?
A curved line indicating that changes in concentration lead to unequal changes in the rate of reaction.
What is the rate determining step in a multi-step reaction?
The slowest step in the reaction mechanism that limits the overall rate of the reaction.
How can speeding up the rate determining step affect the overall reaction rate?
By increasing the rate of the slowest step, the overall rate of the reaction can be significantly increased.
What types of substances can appear in a rate equation?
Reactants and catalysts that affect the rate of reaction.
What is the significance of a species appearing in the rate equation?
It indicates that the species is involved in the rate determining step of the reaction.
Fill in the blank: The overall reaction is a + b + e will give ______.
f + g
True or False: Catalysts can appear in the rate equation even though they are not reactants.
True
What is a common example of a color change reaction that can be monitored?
The reaction between iodine and starch, where iodine changes from brown to colorless.
What must be done to create a calibration curve for measuring iodine concentration?
Make standard solutions of different concentrations and measure their absorbance.
What does an increase in the steepness of a rate concentration graph indicate?
That the reaction is of higher order, specifically second-order.
What is the impact of temperature on the rate of reaction?
Increasing temperature generally increases the reaction rate.
What is the relationship between the gradient of a concentration-time graph and the rate of reaction?
The gradient at any point gives the rate of reaction at that concentration.
What must be included in the rate equation if it is in the rate determining step?
Elements affecting the rate
If an element is in the rate determining step, it must appear in the rate equation.
What does a coefficient of 2 in the rate equation indicate about the order of the reaction with respect to that element?
Second order
A coefficient indicates the power in the rate equation, determining the reaction order.
What is the rate equation derived from the reaction involving elements A, B, and C?
Rate = k [A][B][C]^2
This indicates first order with respect to A and B, and second order with respect to C.
What role does element C play if it does not appear in the overall equation?
Catalyst
C being absent from the overall equation suggests it acts as a catalyst.
What type of catalysis is indicated when an intermediate is formed during a reaction?
Auto catalysis
This occurs when a product of the reaction acts as a catalyst for the reaction itself.
What is the first step to finding the rate determining step from a given reaction?
Identify the ratio of molecules in the rate equation
This involves matching the ratio with the reaction steps to determine the rate determining step.
In the reaction where rate = k [N2][O2]^2, what must you account for in the reaction steps?
The required molecules must match the ratio in the rate equation
This involves identifying steps that provide the necessary reactants in the correct proportions.
What is the significance of the Arrhenius equation?
Links activation energy and temperature to the rate constant K
The Arrhenius equation provides insight into how temperature and activation energy affect reaction rates.
What happens to the rate constant K as activation energy decreases?
K increases
A lower activation energy means a higher likelihood of successful collisions.
What effect does increasing temperature have on the rate constant K?
K increases
Higher temperatures lead to more kinetic energy in particles, increasing collision frequency.
What is the general form of the Arrhenius equation?
K = A * e^(-Ea/RT)
Where K is the rate constant, A is the Arrhenius constant, Ea is the activation energy, R is the gas constant, and T is temperature in Kelvin.
How do you calculate the activation energy using the Arrhenius equation?
Rearrange to EA = R * T * (Ln A - Ln K)
This involves substituting values into the simplified form of the Arrhenius equation.
What is the relationship between the gradient of an Arrhenius plot and activation energy?
Gradient = -Ea/R
The slope of the graph of Ln K against 1/T provides the activation energy when rearranged.
What does the y-intercept of the Arrhenius plot represent?
Ln A
The y-intercept in an Arrhenius plot corresponds to the natural logarithm of the Arrhenius constant.
What does the ‘Ln’ in the Arrhenius equation refer to?
Natural logarithm
It is used to simplify the equation for easier calculations.
What is the activation energy if the gradient of an Arrhenius plot is -11400 and R is 8.314?
EA = -(-11400) * 8.314
This calculation yields the activation energy in joules per mole.
What is the formula to calculate the Arrhenius constant A from the Arrhenius equation?
A = e^(Ln K + (Ea/RT))
This involves substituting the known values into the rearranged Arrhenius equation.
What is the process to isolate Ln a in the equation?
Rearrange the equation to get Ln a on its own, resulting in Ln a = -4 + 34.1
What is the calculated value of Ln a?
30.1
What is the next step after finding Ln a?
Use the exponential button (shift Ln) to find a
What value do you input to find the constant a?
30.1
What is the resulting value of the Arenas constant?
1.18 times 10 to the 13 DM cubed multiplied by s to the minus 1
True or False: The process involves using a calculator to find the value of a after calculating Ln a.
True
What type of reaction is being discussed in the content?
A very fast reaction
Fill in the blank: The final value of the Arenas constant is _____ DM cubed multiplied by s to the minus 1.
1.18 times 10 to the 13
What additional resource is mentioned for further understanding?
A whiteboard video on Arenas plot
