Rate Equations Flashcards

Rate Equations

A-Level AQA Chemistry

This pack of flashcards covers the principles of chemical kinetics, focusing on the rate equation, reaction orders, and experimental determination of reaction rates. It includes the significance of reactant concentration, initial rate method, clock reactions, and temperature's effect on rate constants, as well as the Arrhenius equation and reaction mechanisms.

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Describe the unit of the Arrhenius constant A.	The unit of the Arrhenius constant A will be the same as the unit of the rate constant k.
How does the rate change when the concentration of reactant X doubles?	When the concentration of reactant X doubles, the rate also doubles.
What is the overall order of the reaction?	The overall order of the reaction is third order.
How does increasing the temperature affect the value of the rate constant?	Increasing the temperature increases the value of the rate constant.
Define zero order reaction.	A zero order reaction is a reaction in which the rate stays constant as the reactant is used up.
What is the value of the rate constant for a zero order reaction?	The value of the rate constant for a zero order reaction is equal to the gradient of the concentration-time graph.
Describe the relationship between the concentration of a reactant and the rate in a zero order reaction.	In a zero order reaction, the concentration of a reactant has no effect on the rate.
Describe the effect of temperature on the rate constant.	Increasing the temperature increases the value of the rate constant k.
Define the Arrhenius equation.	The Arrhenius equation is given by k = Ae-EA/RT, where A is the Arrhenius constant, R is the gas constant, and EA is activation energy.
What is the unit of temperature in the Arrhenius equation?	The unit of temperature in the Arrhenius equation is Kelvin (K).
How is the Arrhenius equation usually rearranged?	The Arrhenius equation is usually rearranged to Ink=InA-EA/RT.
Describe the units of activation energy.	Activation energy should be in J mol-¹ to match the units of R.
Do you need to know how to rearrange the Arrhenius equation?	Yes, you should be able to do rearrangements and substitute values into both the original and rearranged equations.
What is the rate equation for the reaction between X and Y?	The rate equation for the reaction between X and Y is r = k [X][Y]^2.
Describe how to calculate the activation energy graphically from experimental data.	Plot a graph of ln(rate) or ln(k) against 1/T. Measure the gradient of the line and multiply it by the gas constant (R) to obtain the activation energy (EA).
What is the relationship between the rate constant (k) and the rate of reaction?	The rate constant (k) is proportional to the rate of reaction.
Define activation energy (EA).	Activation energy (EA) is the minimum energy required for a chemical reaction to occur.
How can the activation energy be calculated using the graph?	The activation energy can be calculated by measuring the gradient of the ln(rate) or ln(k) versus 1/T graph.
Describe the unit of activation energy (EA) obtained using the given equation.	The unit of activation energy (EA) obtained using the given equation is J mol-¹. It can be converted to kJ mol-1 by dividing by 1000.
Describe a rate-determining step in a reaction mechanism.	The rate-determining step is the slowest step in a reaction mechanism and controls the overall rate of the reaction.
Define molecularity in the context of a reaction mechanism.	Molecularity refers to the number of moles of each substance involved in the slowest step of a reaction mechanism.
What is the order of reaction for a substance if it appears as 0 moles in the slow step of a reaction mechanism?	If a substance appears as 0 moles in the slow step, it is considered to be zero order.
How can the rate equation be modified when an intermediate compound is involved in a reaction mechanism?	The rate equation must be modified to include the substances that make up the intermediate compound in a previous step of the mechanism.
Describe the Sn2 mechanism in nucleophilic substitution reactions.	The Sn2 mechanism is a one-step mechanism where the nucleophile attacks the substrate at the same time as the leaving group departs.
How can the change in volume of a gas be measured to determine the rate of reaction?	The change in volume of a gas can be measured using a gas syringe. This method is suitable for measuring continuous rate, but the gas syringe typically measures up to 100ml of gas.
What does the symbol 'r' represent in the rate equation?	The symbol 'r' represents the rate of reaction.
What do the square brackets '[A]' mean in the rate equation?	The square brackets '[A]' represent the concentration of reactant A.
What is the unit of 'r' in the rate equation?	The unit of 'r' is usually mol dm-3 s-1.
What is the rate constant 'k' in the rate equation?	The rate constant 'k' is a proportionality constant that relates the rate of reaction to the concentration of reactants.
What is the total order for a reaction?	The total order for a reaction is determined by adding all the individual reaction orders together.
How are the reaction orders determined?	The reaction orders are determined experimentally and are not the same as the stoichiometric coefficients in the balanced equation.
How can the unit of k be calculated?	The unit of k can be calculated by rearranging the rate equation, inserting the units, and simplifying the fraction.
Describe the concept of continuous monitoring in relation to rate of reaction.	Continuous monitoring refers to following one experiment over time and recording the change in concentration. The gradient of the concentration-time graph represents the rate of reaction.
What is the significance of having a large excess of reactants in a reaction?	In reactions with several reactants, if one reactant is kept in a large excess, it will appear to have no effect on the rate and will be pseudo-zero order. This is because its concentration stays virtually constant and does not affect the rate.
What is a common clock reaction?	A common clock reaction involves two successive reactions, where the end point is achieved when one limited reactant runs out, resulting in a sudden color change.
How can the order of reaction be determined in a clock reaction?	By repeating the experiment several times and varying the concentration of a reactant while keeping the other reactants at constant concentration, the order of reaction with respect to that reactant can be determined.
How can the of a reaction be calculated graphically?	By plotting a graph of log rate vs log [Y], where Y is the concentration of one of the reactants that is changed, the gradient of the line obtained is equal to the order of the reaction.
Define the term 'order' in the context of a rate equation.	The order of a reactant in a rate equation represents the power to which its concentration is raised in the rate equation.
What is the significance of high concentrations and quick times in experimental initial rate data?	High concentrations and quick times in experiments can lead to the biggest percentage errors in the initial rate data.
Describe the effect of changing the concentration of both reactants simultaneously on the rate of a reaction.	The effect of changing the concentration of both reactants simultaneously is that the individual changes in concentration are multiplied together to give an overall change in the rate of the reaction.

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