# Reaction steps and Activation Energies

• engineer23
In summary, the overall activation energy E is 60 kcal/mol and the reaction steps are CH3CHO --> .5CH3CO + .5CH3 + .5H2 (E1 = 80 kcal/mol), CH3CO --> CH3 + CO (E2 = ?), CH3 + CH3CHO --> CH4 + CH3CO (E3 = 10 kcal/mol), and CH3 + CH3CO --> minor products (E4 = 5 kcal/mol). Using the equation E1 + E2 + E3 + E4 = E, E2 can be estimated to be -35 kcal/mol. A negative activation energy means that the reaction will take place and cannot be stopped. The Arrhen
engineer23

## Homework Statement

The overall activation energy E is 60 kcal/mol.
Reaction steps are:
CH3CHO --> .5CH3CO + .5CH3 + .5H2 E1 = 80 kcal/mol
CH3CO --> CH3 + CO E2 = ?
CH3 + CH3CHO --> CH4 + CH3CO E3 = 10 kcal/mol
CH3 + CH3CO --> minor products E4 = 5 kcal/mol

Estimate E2.

## Homework Equations

Arrhenius equation k = A exp (-E/RT)

## The Attempt at a Solution

Does E1 + E2 + E3 + E4 = E? If so, then E2 = -35 kcal/mol. If this is the case, what does negative activation energy mean (physically)?

Do I need to use the Arrhenius equation and/or d[M]/dt expressions to solve this problem. Since E1 >> E3 and E4, are there any assumptions I can make?

I feel like I'm missing something here.

Thanks!

I am almost positive that if you have a negative activation energy that it means that the reaction will take place and that it will not be possible to stop it.

Hope this helps.

Steve

it is important to carefully consider the information given and make logical deductions based on established principles and equations. In this case, the given information suggests that the overall activation energy (E) for the reaction is 60 kcal/mol. The reaction is also described in terms of four individual steps, each with their own activation energy (E1, E2, E3, and E4).

Based on the given information, it is reasonable to assume that the activation energies for the individual steps add up to the overall activation energy. Therefore, E1 + E2 + E3 + E4 = E. Using this equation, we can solve for E2 by rearranging the equation to E2 = E - E1 - E3 - E4. Substituting in the given values, we get E2 = 60 kcal/mol - 80 kcal/mol - 10 kcal/mol - 5 kcal/mol = -35 kcal/mol.

A negative activation energy is not physically meaningful, as activation energy is defined as the minimum energy required to initiate a reaction. In this case, a negative activation energy would suggest that the reaction does not require any energy to proceed, which is not possible. This indicates that there may be an error in the given information or that the reaction steps are not representative of the actual reaction.

The Arrhenius equation can be used to calculate the rate constant (k) for a reaction, but it requires the activation energy (E), the pre-exponential factor (A), the temperature (T), and the gas constant (R). Since the given information does not provide all of these values, we cannot use the Arrhenius equation to solve for E2.

In terms of assumptions, we can assume that the overall activation energy is the sum of the individual activation energies, and that the rate constant for each step is proportional to the concentration of the reactants. However, these assumptions may not be accurate if the given information is not representative of the actual reaction.

In conclusion, based on the given information, we can estimate that E2 = -35 kcal/mol, but this value is not physically meaningful. It is important to carefully consider the given information and make logical deductions, but in cases where the information is incomplete or inaccurate, it may not be possible to accurately solve for all parameters.

## 1. What is a reaction step?

A reaction step is a single event that occurs during a chemical reaction. It involves the breaking and formation of chemical bonds between reactant molecules to produce products.

## 2. What is activation energy?

Activation energy is the minimum amount of energy required for a chemical reaction to occur. It is the energy barrier that must be overcome for the reactants to turn into products.

## 3. Why is activation energy important?

Activation energy is important because it determines the rate at which a chemical reaction takes place. The higher the activation energy, the slower the reaction will be. It also controls the selectivity of a reaction, meaning the specific products that are formed.

## 4. How can activation energy be lowered?

Activation energy can be lowered by using a catalyst. A catalyst is a substance that speeds up a chemical reaction by providing an alternative pathway with a lower activation energy. This allows the reaction to occur more quickly and with a lower energy input.

## 5. What factors affect reaction steps and activation energies?

The factors that affect reaction steps and activation energies include the nature of the reactants, temperature, concentration, and the presence of a catalyst. The type of reaction and the physical conditions also play a role in determining the activation energy.

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