Determining the rate law from experimental data

In summary: If not then the data is not consistent and the reaction order cannot be determined.In summary, the conversation discusses a problem involving the initial rates method and determining the most plausible answer from multiple possible solutions. The question is about knowing which solution is correct when solving these types of problems. The solution involves comparing ratios and plugging in the concentration of a reactant with its order to determine consistency.
  • #1
fridakahlo
10
1

Homework Statement


First question on PDF:
http://ars-chemia.net/Classes/102/Problem_Sets/Practice Exam for Exam 1 Key.pdf

Homework Equations


I used the initial rates method:
Rate2/Rate1=k2*[A]^m/k1*[A]^m

The Attempt at a Solution


When I solve these types of problems with the initial rates method, I get multiple possible solutions. For instance, for reactant B, I got -2.5 when comparing rates 3 and 2, but when comparing rates 3 and 1 I got -0.5. I know the answer is -0.5.
My question is how do I know which one is the most plausible answer when solving these types of problems?
 
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  • #2
It was rather hard for me to make out what your question is. I guess it is about Question 1? This appears to be solved correctly, I presume the answers in red are yours? What is written above though does not correspond to this answer.
 
Last edited:
  • #3
fridakahlo said:

Homework Statement


First question on PDF:
http://ars-chemia.net/Classes/102/Problem_Sets/Practice Exam for Exam 1 Key.pdf

Homework Equations


I used the initial rates method:
Rate2/Rate1=k2*[A]^m/k1*[A]^m

The Attempt at a Solution


When I solve these types of problems with the initial rates method, I get multiple possible solutions. For instance, for reactant B, I got -2.5 when comparing rates 3 and 2, but when comparing rates 3 and 1 I got -0.5. I know the answer is -0.5.
My question is how do I know which one is the most plausible answer when solving these types of problems?
you take any ratio ...answer should be same
If you take R1/R3 then [A] is canceled and if you do R3 and R1 then plug in the conc of A with raise to power of its order .. it should give us the same answer ...
 

1. What is the rate law and why is it important in science?

The rate law is a mathematical equation that describes the relationship between the concentrations of reactants and the rate of a chemical reaction. It is important in science because it allows us to predict and control the rate of a reaction, which is crucial in many fields such as pharmaceuticals, materials science, and environmental science.

2. How do you determine the rate law from experimental data?

To determine the rate law, experimental data is collected by varying the concentrations of reactants and measuring the rate of the reaction at each concentration. Then, the data is analyzed using the method of initial rates or the method of integrated rate laws to determine the rate constant and the orders of each reactant.

3. What is the difference between the method of initial rates and the method of integrated rate laws?

The method of initial rates involves measuring the initial rates of a reaction at different concentrations of reactants and using this data to determine the orders of each reactant. The method of integrated rate laws involves plotting the concentration of a reactant over time and using the slope of the line to determine the order of that reactant. Both methods can be used to determine the rate law, but the method of initial rates is more accurate for reactions with complex mechanisms.

4. Can the rate law change over time?

No, the rate law is a constant value for a specific reaction at a given temperature and pressure. However, the rate constant may change over time due to factors such as changes in temperature or the addition of a catalyst.

5. How does a catalyst affect the rate law of a reaction?

A catalyst can change the rate law of a reaction by providing an alternative pathway with a lower activation energy. This results in a faster rate of reaction and can change the orders of the reactants in the rate law equation.

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