Topic 16
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What can rate expressions also be called?
Rate law or rate equation
What do rate expressions tell us?
The rate of a reaction as a function of the reactant concentrations
What is the equation for rate?
Rate= K {A}x [B}y ( x and y are superscript) • K= rate constant • X= order of reaction with respect to A • Y= order of reaction with respect to B
What is K?
The rate constant
How can the overall rate of a reaction be shown?
X+Y
Write a balanced equation for the reaction of nitrogen monoxide and ozone and determine the rate expression
NO+ O3 –NO2+ O2 Rate = K[NO][O3] - 1st order with respect to NO and O3
How only can components of a rate expression be determined?
Experimentally
What are the 3 aspects of determining the rate expression?
• Initial rates are calculated using concentration measurements • The orders of a reaction are calculated using initial rates from several experiments • Initial rate and orders of a reaction are used to calculate the value of the rate constant
Describe elementary steps
• The reaction can happen in a series of steps - The sequence of these steps are reaction mechanisms
What does the rate of a reaction depend on?
The rate determining step which is the slowest
What is a reaction intermediate?
An element that is produced in one step and consumed in another ( one on left hand side of equation, one on the right)
What is the criteria for a reaction mechanism?
• The elementary steps must be reasonable ( unimolecular or biomolecular) • the sum of the elementary steps must add up to the overall equation • the rate expression of the rate determining step must be equal to the one calculated experimentally
What do unimolecular equations have?
• One reactant particle
What do bimolecular reactions have?
Two reactant particles
What is the role of a catalyst?
Increases the rate of a chemical reaction by providing an alternative pathway with a lower activation energy
What happens to the rate constant when activation energy is lowered?
Increases and alters the reaction mechanism
What method is used to determine the order of a reaction?
The initial rates method
What does it mean when the concentration of an element is doubled and the inital rate increases by a factor of 4?
THe reaction is 2nd order with respect to that element
What happens when the concentration of an element is doubled and the intital rate is also doubled?
The reaction is 1st order with respect to that element
What happens when changing the concentration has no effect on the rate of a reaction?
The reaction is zero order with respect to that element
What does not appear in the overall chemical reaction?
The reaction intermmediates
Draw an energy level diagram showing the transition states
What exists between a reactant and product and forms an activated complex?
Transition states
Draw a 1st order rate of reaction graph