7. (a) (i) Define rate of a reaction - Leaving Cert Chemistry - Question 7 - 2018

The activation energy is the minimum energy required by colliding particles to initiate a chemical reaction. It is essential for overcoming the barrier that holds the reactants together, allowing them to transform into products.

Plot the concentrations of NO_2 and O_2 against time on the same axes, ensuring the NO_2 concentration shows a decreasing trend while the O_2 concentration increases. The curves should be smooth and demonstrate the relationship between the two concentrations over time, illustrating that as NO_2 decreases, O_2 increases.

To find the instantaneous rate at 100 seconds, we can draw a tangent to the concentration-time graph at this point and use the slope of the tangent line. From the given data, using points at 100s (0.0065 M) and 50s (0.0079 M):

$\text{Instantaneous Rate} = \frac{0.0065 - 0.0079}{100 - 50} = \frac{-0.0014}{50} = -2.8 \times 10^{-5} M s^{-1}$

Not every collision between NO_2 molecules results in the formation of products because the colliding molecules may not have sufficient energy to overcome the activation energy barrier, or they may not be oriented correctly for a reaction to occur.

One way to increase the frequency of collisions is to raise the temperature of the reaction mixture, which causes the molecules to move faster, leading to more frequent collisions.

The profile diagram should illustrate the energy changes during the reaction. It should show reactants having higher energy than products with an activation energy peak in between. The x-axis represents the progress of the reaction, while the y-axis depicts the energy level. Label the reactants, products, and the activation energy clearly.