Enthalpy of change Questions and Answers

What factor does not affect the rate of chemical reaction?
The enthalpy change of the reaction


In the energy digram for a chemical reaction is shown below. Which letter correctly represents the activation energy for the catalyzed reaction in the forward direction?
C

The rates of many reactions approximately double with temperature increase of 10 degrees. This is best attributed to a doubling of the fraction of molecules that have the energy needed for reaction 

Reactions between aqueous solutions of sodium thiosulfate and acid can be followed by timings the appearance of the solid sulfur that is produced. The time required for the appearance of the sulfur would increase by the change of the following diluting the solution.


Correct balancing of the equation
CaC03 (s) + 2HCl (aq) ----> CaCl2 (aq) + H20 (l) + C02 (g)

7.1.1

7.1.1
Outline the characteristics of chemical and physical systems in a state of equilibrium. 
Equilibrium is the when the products and reactants are at a constant ratio. The state of forward and backward reaction are at the same rate.


Physical System
At room temperature, a bottle of Bromine( a liquid at room temperature) is sealed. Because Bromine is a volatile liquid, its boiling point is close to room temperature.

Some Bromine particles will have enough energy to vaporize, at the same time, the vaporized particles will collide with the surface of the liquid, allowing it to lose energy and become liquid. Because the rate of evaporation is equal to the rate of condensation, there is no net change in the amount of liquid and gas present. So, the system has reached equilibrium


Chemical System
Iodine releases a purple gas, and Hydrogen and Hydrogen Iodide are both colorless.
If an experiment is carried out with Hydrogen Iodide in a sealed container. There will be an increase in the color purple, but after a while, the increase in the color will stop. It may seem that the reaction has stopped too, however, what actually happened is that the rate of dissociation of Hydrogen Iodide has become equal to the reverse rate of reaction of the association of Hydrogen gas and Iodine gas.
Therefore equilibrium has been reached. There is no net change observed even though both reactions are taking place.

A experiment was carried out in class to prove that Copper Sulfate (CuS04) goes through a state of equilibrium at room temperate.

Before the experiment 

- The piece of hydrous copper sulfate was taken from a sealed bottle (as seen in the picture, the copper sulfate is very blue)
-The piece of copper sulfate was then heated under a bunsen burner
-After heating the hydrous copper sulfate for a while, the copper sulfate became white
- The copper sulfate was then left alone for a while
- The copper sulfate started to change color for white to blue, proving that the water from the atmosphere was absorbed back into the copper sulfate.

After Heating the Copper Sul

It is proven that at room temperature, when hydrous copper sulfate is left alone, it is at a state of equilibrium. Because after it is heated, the copper sulfate will start absorbing the water from the atmosphere, but when left alone, the color does not change.

6.2.5, 6.2.6 & 6.2.7

6.2.5
Sketch and explain qualitatively the Maxwell-Boltzmann energy distribution curve for the fixed amount of gas at different temperatures and the consequences for changes in reaction rates. 
Particles in gases at different temperatures have differen

t kinetic energy, and it is expressed using the Maxwell-Boltzmann distribution curve (below).

The curve proves that the value of kinetic energy varies from one reaction to another. The curve proves the rate of reaction depends on the particles that have values of kinetic energy greater than the activation energy.





6.2.6
Describe the effect of the catalyst  on a chemical reaction. 
A catalyst is a substance increases the rate of reaction without itself going through permanent changes.
It works by providing an alternative route for the reaction.

Without the increase of temperature, the a large amount of particles will have a greater kinetic energy than the activation energy, so there will be a successful collision of particles.










6.2.7

The video where water is used as a catalyst to speed up the reaction between the reactants, Aluminum and Iodine. 

6.2.4

Predict and explain using the collision theory, the qualitative effects of particles size, temperature, concentration and pressure on the rate of reaction. 


1. Temperature
As temperature increases, the rate of reaction also increases. This is because increases in temperature causes the increase in kinetic energy, thus increasing the energy in particles, causing them to collide into each other more quickly.

The area under both of the graphs are the same. However, the rate of reaction and the time taken varies. The peak of the curve shifts to the right, the higher the temperature, the more the energy, and the higher the activation energy. 

2. Concentration

The higher the concentration, the more the particles present in the same area. Therefore there will be a higher chance in which the particles will bump into each other. 

3. Particles size

Decreasing the particle size, increases the chances of collision. The smaller the size of the particle, the higher the surface area, and the chances for it to get into contact with another particle. 

4. Pressure

For objects in the gaseous state, by increasing the pressure, the collision increases. This because, increase in pressure, causes the gas to compress, this results in the higher concentration of gas. Allow more collision between particles, increasing the rate of reaction. 

An experiment was carried out using the different sizes of marble chips in acid. 

Independent variables: the size of the marble chips 

Dependent variables: Time taken for the reaction to complete

Controlled variables: temperature, concentration of acid, pressure of surrounding

The amount of time taken for the rate of reaction varies between the different marble chips, due to the difference in the particle sizes and surface area. 

6.2.2 & 6.2.3

6.2.2

Define the term activation energy Ea

<sub>The minimum value of kinetic energy, for a collision to lead to a reaction, is necessary to overcome repulsion between molecules and often to break some bonds in the reactants before they react. When the energy is supplied, the reactant achieve the transition state from which products can form. The energy required represents an energy barrier for the reaction and is known as activation energy. 


6.2.3
Define collision theory</sub> 
The rate of reaction depending on the frequency of collision which occur between particles processing both values of kinetic energy greater than the activation energy or appropriate collision geometry.