Rate of Reaction and Chemical Kinetics Flashcards

Comprehensive practice questions covering reaction rates, experimental methods, collision theory, Maxwell-Boltzmann distributions, and the Arrhenius equation.

How is the instantaneous rate of a reaction determined at a particular time ($t_1$)?

It is determined by calculating the slope of the tangent to the concentration-time curve at that specific time.

When calculating the rate of disappearance of a reactant, what must be introduced to ensure the rate value remains positive?

A minus sign must be introduced.

What does the slope of the curve represent in a graph of product volume over time?

The slope represents the rate of reaction.

Why is the rate of reaction curve generally steepest at the start ($t = 0$)?

The concentration of reactants is at its highest, meaning the initial rate of reaction is the fastest.

Why does the reaction rate curve eventually become horizontal (slope = $0$)?

One of the reactants has been used up, causing the reaction to finish.

What is the purpose of placing a reactant like $CaCO_3$ in a small test tube or on a thread inside a reaction flask?

To keep the two reactants separated while setting up the apparatus so that the start time can be accurately recorded.

Define 'Reaction Rate' based on concentration and time.

Reaction rate is the change in the amount or concentration of a reactant or product per unit time.

What are three limitations of using gas syringes or measuring cylinders to measure reaction rate?

1. Limited precision; 2. Gas leakage or incomplete collection (e.g., gas dissolving in water); 3. Temperature fluctuations affecting gas volume.

What is the purpose of plugging a conical flask with cotton wool during mass-loss experiments?

To prevent droplets of water or acid spray from escaping due to spurting, while still allowing gaseous products to leave the flask.

Why cannot the change in mass method be used to measure the rate of a reaction that produces hydrogen ($H_2$) gas?

Hydrogen is too light, resulting in no significant change in mass that can be measured accurately.

In colorimetry, what is the relationship between light absorbance and the concentration of colored species?

Light absorbance is directly proportional to the concentration of colored ions.

What are the limitations of the colorimetry method?

1. It can only be used for reactions with a visible color change; 2. Interference from other colored substances or solids; 3. Limited concentration range for the linear relationship.

What is 'quenching' in the context of titration experiments?

Quenching is the process of stopping the reaction from proceeding by adding cold water, removing a catalyst, or placing the mixture in an ice bath.

In the titration of iodine ($I_2$) against sodium thiosulfate ($Na_2S_2O_3$), what is the color change at the end point?

The color changes from dark blue to colourless when using starch as an indicator.

According to collision theory, what two criteria must be met for a reaction to occur?

1. Particles must collide with sufficient energy (energy $\geq E_a$) to break bonds; 2. Particles must collide with the correct orientation.

How does increasing temperature affect the number of effective collisions?

It increases the kinetic energy of molecules, leading to a higher frequency of collisions and a greater proportion of molecules with energy $\geq E_a$.

Define 'Activation Energy' ($E_a$).

The minimum energy needed for a reaction to occur by overcoming repulsion and breaking existing bonds.

How do the activation energies of forward and reverse reactions compare in an exothermic reaction?

The activation energy of the forward reaction is lower than the activation energy of the reverse reaction.

List four key features of a Maxwell-Boltzmann distribution curve.

1. It is not symmetrical; 2. Total area is proportional to the total number of particles; 3. It starts at the origin; 4. It never touches the x-axis at high energy.

Describe the difference between homeogeneous and heterogeneous catalysts.

Homogeneous catalysts are in the same state as the reactants, whereas heterogeneous catalysts are in a different state.

What factor causes an exponential increase in the value of the rate constant ($k$)?

.

An increase in temperature

What is the half-life ($t_{1/2}$) formula for a first-order reaction?

$$t_{1/2} = \frac{\ln(2)}{k}$$

What is the 'rate-determining step' ($RDS$) of a reaction mechanism?

The slowest step in a reaction pathway which has the highest activation energy and limits the overall rate.

In the Arrhenius equation ($k = A e^{-E_a/RT}$), what does the factor $A$ represent?

The Arrhenius factor (or frequency factor), which accounts for the frequency and orientation of collisions.

How can the activation energy ($E_a$) be determined from a graph of $\ln(k)$ against $\frac{1}{T}$?

The slope of the line is equal to $-\frac{E_a}{R}$, where $R$ is the gas constant.