Topic 8:Acids and Bases

7.2.2

I can deduce the extent of a reaction from the magnitude of K_c

1. What does the word magnitude mean?

2. Explain why the three reactions above do not have units for K_c

3. Deduce the extent of the reaction if K_c is

a. significantly larger than 1

b. between 0.01 and 100

c. extremely small

1)The word magnitude means size.
2)The reactions do not have units for the value of Kc because the sum of the moles of products equals to the sum of the moles of the reactants.
3)a) If its much larger than 1, this shows that reaction is yielding a lot of products.
   b)If its between 0.01 and 100, this shows that theres a lot of products and reactants.
   c)It its extremely small, this shows that nothing much is happening.

7.2.1

I can deduce the equilibrium constant K_c for homogenous reactions:

3.       Answer the following questions:

a.      What can change the value of K_c

b.     The reaction must be at ____________ for the value of K_c to be calculated

c.      Define the term homogeneous

d.    Rule for unit of Kc

a)The value of Kc can only be changed by changing the temperature.
b)The reaction must be at equilibrium for the value of Kc to be calculated.
c)The term homogeneous means when the products and the reactants are all in the same state.
d)(c+d)-(a+b)=0, then no units
    (c+d)-(a+b)=1, then unit of moldm-3
    (c+d)-(a+b)=-1, then unit of mol-1dm3

Targets

I would like to focus more on the rates of reaction, specifically the Boltzman Maxwell distribution curve and how the rate of reaction changes as a reaction progresses.

7.1.1

I can outline the characteristics of chemical and physical systems in a state of equilibrium.

Equilibrium- a reaction in which the rate of the forward reaction is equal to the rate of the backward reaction. The concentrations of reactants and products are constant as well.

Examples of dynamic equilibrium



This is an example of an dynamic equilibrium in the physical system.
Bromine is a volatile liquid so many particles have enough energy to escape from the liquid state to form vapour. But at the same time, some of the vapour molecules collide with the surface of the liquid thus lose liquid and become a liquid. There is no net change between the amounts of gas and liquid.



This is an example of a chemical system. The reaction of dissociation between hydrogen iodide and its elements hydrogen and iodine. At the start of the reaction, there is an increase in purple due to the production of iodine gas but after the while there is no more change. At the stage, it could be said that equilibrium has been reached since there is no net change between the concentrations of the products and reactants.

We were observing a dynamic equibrilium occuring in copper sulphate. Hydrated copper sulphate appears as blue whilst anhydrous copper sulphate turns white. This could be used as a test for water, but not for pure water just for any substance that contains water. When hydrated copper sulphate is heated, it turns white and when water is added back in again it turns blue.

IB Question answers

1)D
2)A
3)D
4)B
5)C
6)B
7)C

11)a) To measure the rate of reaction, you can measure the mass of the reactants against time, measure the volume of carbon dioxide produced against time and measure the pH of the solution against time.

    


b)To increase the rate of reaction, you can increase the temperature which provides particles with more kinetic energy than the activation energy so the collision frequency increases. Using a catalyst provides an alternative route with a lower activation energy thus the rate of reaction increases. Lastly, increasing the concentration of the acid would speed up the reaction because there would be a higher collision frequency.

c)i)The volume produced stays the same because the lumps of magnesium are already in excess thus there is no effect on the reaction.

ii) The volume produced stays the same when temperature is increased because temperature increases the rate of reaction but the concentrations stay the same.

6.2.5,6.2.6 and 6.2.7

6.2.5 Sketch and explain qualitatively the Maxwell–Boltzman energy distribution curve for a fixed amount of gas at different temperatures and its consequences for changes in reaction rate.

Increasing the temperature increases the rate of all reactions because particles have greater kinetic energy thus meaning more particles have kinetic energy exceeding the activation energy. The graph above shows to similar curves because area is proportional to the total number of particles. But when increasing the temperature, the peak of the curve shifts right resulting in an increase in collision frequency and thus more successful collisions. However the area remains the same because the number of particles doesn't change. Area shows the number of particles.

6.2.6 Describe the effect of a catalyst on a chemical reaction.

The effect of adding a catalyst is that the rate of reaction increases however the catalyst remains unchanged. Catalysts work by providing an alternative route which has lower activation energy so this speeds up the reaction as more particles have more kinetic energy than the activation energy.

6.2.7 Sketch and explain Maxwell– Boltzmann curves for reactions with and without catalysts.

Catalysts increase the proportion of particles that have values for kinetic energy greater than the activation energy.

6.2.4

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

Independent variables	Time, Surface area of marble chips
Dependent variable	Volume
Controlled variables	Mass of marble chips, Concentration and volume of hydrochloric acid, Temperature of surroundings, Volume of water in the inverted measuring cylinder
Collision theory explanations	The larger the surface area, the faster the reaction should be because in a powdered solid, the particles can easily come into contact with the surrounding reactant. But in solid substance, only the particles on the surface can come into contact with a surrounding reactant. So as surface area increases, rate increases dramatically too.
Gradient represents:	Rate of reaction
Units for gradient	cm3/sec
Reasons for differences in graphs	The results don’t exactly support the collision theory otherwise the line for the powder would be the steepest showing the fastest rate of reaction. However, for other types of marble chips the line is steeper as the surface area increases.

6.2.2 and 6.2.3

6.2.2 Define the term activation energy, Ea.

6.2.3 Describe the collision theory.


1) The more frequent the collisions the faster the reaction.
2) In order to react, particles must have a minimum kinetic energy in order to overcome the repulsion between molecules and to break bonds become reacting to become products.
3) If the molecules dont react in appropriate orientation, a reaction wont take place.

Activation energy	Activation energy is the minimum value of kinetic energy which particles must have before they are able to react.
Three factors that affect the rate of reaction:	1)      Collision frequency
	2)      Number of particles having greater kinetic energy than activation energy
	3)      Appropriate collision geometry

6.2.1

6.2.1 Describe the kinetic theory in terms of the movement of particles whose average energy is proportional to temperature in Kelvin.

 I can describe kinetic theory:

Temperature is kelvins is proportional to the average kinetic energy of the particles in a substance. Basically, kinetic energy is the reason particles are able to move randomly.

The picture shows a kinetic theory apparatus. The kinetic theory apparatus has two cardboard pieces which represents volume and beads that are given energy by increasing the voltage. Increasing the voltage is an analogy of increasing the temperature. As the temperature is increased, particles have more kinetic energy therefore move faster and collide with the insides of the container and cardboard more often causing the cardboard pieces to go up. This shows an increase in volume.

6.1.3

6.1.3: Analyse data from rate experiments. Graphs of changes in concentration, volume or mass against time should be interpreted qualitatively.

6.1.2

6.1.2 Describe suitable experimental procedures for measuring rates of reactions

Experimental Method	Dependent and Independent variables	Diagram	Additional Notes
Change in volume of gas produced	Independent: time (sec) Dependent: volume of gas (cm3)		Gas syringe best because inverted measuring cylinder or burette limited to gases with low solubility
Change in mass	Independent: time(sec) Dependent: mass of reactants(g)		Unlikely to work well, because there might not be a significant decrease in mass for example hydrogen is too light
Change in transmission of light: colorimery/ spectrophotometry	Independent: time(sec) Dependent: light intensity		Only works with coloured compounds, as the concentration of compounds increases, more light is absorbed therefore less is transmitted
Change in concentration measured using titration	Independent: time(sec) Dependent: concentration (cm3)		It cannot be done continuously thus samples must be taken from the reaction mixture. To avoid the mixture over reacting, a method called “quenching” can be used which provides a snap shot at the moment it is withdrawn.
Change in concentration measured using conductivity	Independent: time(sec) Dependent: electrical conductivity		As reactants are converted into products, there’s a sharp decrease in the electricity conductivity as there’s a decrease in the concentration of ions
Non-continuous methods of detecting change during a reaction:”clock reactions”	Independent: time(sec) Dependent: a magnesium ribbon disappearing or a cross view is no longer visible		It is more convenient to measure the time it takes for a reaction to reach a choosen fixed point

6.1.1

6.1.1 Define the term rate of reaction

rate of reaction-the rate of a chemical reaction is an increase in concentration of products to reactions per unit time

My first post