Topic 2 - Managing Chemical Processes

Question 1

What does the rate of reaction refer to?

Answer 1

The rate at which chemical reactions occur overtime.
- can be expressed as the rate at which a product is formed, or the rate at which a reactant is consumed.

Question 2

How is rate of reaction measured?

Answer 2

• Concentration vs time graph.

Question 3

What does the slope represent on a concentration vs time graph?

Answer 3

• The rate at which concentration changes
• This is the slope

Question 4

Where do reactants start of a concentration vs time graph?

Answer 4

Concentration of the reactant (the y-axis)

Question 5

Where do the products start on a concentration vs time graph?

Answer 5

concentration = 0 (the y -axis)

Question 6

How do you find the average rate of reaction and what does this encompass?

Answer 6

• Rise/run of the starting point and end point
• Encompasses the reaction from start to finish

Question 7

How do you find the rate of reaction at a specific time?

Answer 7

• Draw a tangent to that point
• Use the x and y intercepts as x1, x2, and y1, y2.

Question 8

How do you interpret slopes in a rate of reaction graph?

Answer 8

• Steep slope = large slope and shows that the reaction is happening rapidly.
• Shallow slope = small slope and shows that the reaction is happening slowly.
• Zero slope - No reaction is happening or the reaction has met equillirbium.

Question 9

Describe the difference between endo and exothermic reactions in bonds and energy.

Answer 9

Endothermic reaction:
Uses energy to break bonds, and there is a net adsorption of energy from the environment, therefore the temperature of the environment decreases.

Exothermic reaction:
Energy is released when bonds are formed, and there is a net release of energy into the environment, therefore the temperature of the environment increases.

Question 10

Define enthalpy.

Answer 10

Enthalpy is the total energy/heat of the system at constant pressure and volume.

Question 11

What is the equation for change in enthalpy?

Answer 11

AH= H(products)-H(reactants)

Question 12

Draw an exothermic energy profile diagram.

Answer 12

H(products)<H(reactants)
AH<0, therefore enthalpy is negative.

Question 13

Draw an endothermic energy profile diagram.

Answer 13

H(products)>H(reactants)
AH>0, therefore enthalpy is positive.
The activation energy is so high which is why they are less favorable reactions, because they require so much energy to overcome this curve.

Question 14

How is a change of enthalpy in a reaction calculated?

Answer 14

Q=MCAT
AH=Q/n

Question 15

How do successful collisions result in product formation?

Answer 15

The kinetic energy of the colliding particles exceeds the activation energy of the reaction.

Question 16

Why do unsuccessful collisions not result in product formation?

Answer 16

The kinetic energy of the colliding particles is less than the activation energy required for the reaction.
This leads to particles bouncing off each other.

Question 17

What is required for a successful reaction - collision theory?

Answer 17

• colliding particles must have a equal to or greater kinetic energy than activation energy required for the reaction.
• The colliding particles must collide with the correct orientation for a reaction to occur.

Question 18

How does collision theory increase the rate of reaction?

Answer 18

• The rate of a reaction is dependent on the frequency of sucessful collisions.

High frequency of successful collisions - increased rate of reaction
Low frequency of successful collisions - decreased rate of reaction.

Question 19

How do you increase the rate of reaction through collision theory?

Answer 19

• Increase the frequency of successful collisions by:
• Having them frequently collide
• Colliding with the correct orientation
• Colliding with kinetic energy greater than or equal to the activation energy required for the reaction to occur.

Question 20

What factors can alter the RATE OF REACTION?

Answer 20

• Temperature
• Concentration
• pressure
• Surface area
• Catalysis
• Enzymes

Question 21

How does temperature increase the rate of reaction?

Answer 21

The temperature is the overall

Question 22

What is hard water?

Answer 22

• Water with excess concentration of calcium/magnesium ions.

Question 23

What are zeolites?

Answer 23

• porous aluminosilicates composed of SiO4 and arranged in a tetrahedral formation.
• They are customizable in size to the desired ion you are trying to catch.

Question 24

How do zeolites soften hard water?

Answer 24

• Zeolites are used as a cation exchange surface. Hard water is passed through zeolites containing Na+ in the pores. Calcium/Magnesium ions in the water are highly charged and attract to the negatively charged zeolite. Being more highly charged than sodium or potassium, they undergo a cation exchange and displace them out of the zeolite and into the water.

Question 25

What are the three requirements for collision theory?

Answer 25

1. Particles must frequently collide.
2. Particles must collide with the correct orientation.
3. Particles must collide with the correct energy greater than or equal to the activation energy.

Question 26

How does temperature effect collision theory?

Answer 26

Increased temperature: Kinetic energy is the overall heat of the reaction. At increased temperatures particles are moving at a faster rate with a greater kinetic energy. They have a higher chance of colliding provided with the correct energy, therefore increasing the frequency of successful collisions and therefore the rate of reaction.

Decreased temperature: Particles move slower with a lower kinetic energy, decreasing the frequency of successful collisions and therefore the rate of reaction.

Question 27

How does concentration of reactants affect collision theory?

Answer 27

Increased concentration of reactants means there is a greater change of frequent collisions between them as more are available to collide. This increases the rate of reaction.

Question 28

How does pressure affect collision theory?

Answer 28

Increased pressure decreases the volume, therefore trapping gaseous particles in a more confided space. This increases the frequency of collisions as particles are closer together and therefore will collide more frequently. This increases the rate of reaction.

Question 29

How does particle size affect collision theory?

Answer 29

Decreased particle size increase the surface area. Providing a larger surface for collisions to occur increases the chance of frequency of successful collisions. This increases rate of reaction.

Question 30

How does a catalyst increase the rate of reaction?

Answer 30

A catalyst provides an alternate energy pathway by lowering the activation energy.
This lowers the kinetic energy required for successful collisions between particles, and therefore increases the proportion of reactants that meet this requirement.
This increases the frequency of successful collisions and therefore increases reaction rate.

Question 31

How does an enzyme increase the rate of reaction?

Answer 31

Enzymes provide the correct orientation between particles for a successful collision using their active site.
It also provides an alternate energy pathway, lowering the activation energy. This increases the proportion of reactants that poses energy equal to or greater than the activation energy.
This increases the frequency of successful collisions which increases rate of reaction.

Question 32

Describe how hard water renders the use of soap with the aid of an equation.

Answer 32

Hard water contains strongly positively charged calcium/magnesium ions. They bind strongly to the anionic hydrophilic head of soaps structure. This limits this ability to form micelles and dissolve in water as it forms a precipitate. It can no longer attach to grease, therefore limiting its use.

Ca2+(aq) + 2CROO- <—> Ca(RCOO)2.

Question 33

What is the equation for chlorination of water using chlorine gas? And how does adding a base increase its useability?

Answer 33

Cl2(g) + 2H2O(l) <—-> HOCl(aq) + H3O+(aq) + Cl-(aq)

Adding a base neutralizes the hydronium ions. This means there is a decrease in the products, so equilibrium will shift to the right producing more hypochlorous acid, which disinfects the water by killing the bacteria as a strong oxidizing agent.

Question 34

What is the significance in water treatment of hypochlorous acid dissociating in water? Use an equation.

Answer 34

HOCl(aq) + H2O(l) <—-> H3O+(aq) + OCl-(aq).

Hypochlorous acid can disassociate in water to form hypochlorite ions. These (Cl2, HOCl, and ClO) are effective at killing bacteria as they are powerful oxidizing agents that reduce to chloride ions to kill bacteria (Cl-).

Question 35

Which is the best oxidizing agent in disinfecting water?

Answer 35

Hypochlorous acid (HOCl) is the best oxidizing agents because it is the smallest of the three, and is neutral in charge so it can enter through bacterial membranes easily.

Question 36

What method of chlorination of water is commonly used in swimming pools? Use an equation to support your response.

Answer 36

Using salts containing chlorine are common methods to get the chlorine into the water without toxic chlorine gas.

Ca(ClO)2 is one, and NaOCl is another. They both contain spectator ions but both follow the same real equation:

ClO-(aq) + H2O(l) <—–> HOCl(aq) + OH-(aq)

Question 37

What is clay made of?

Answer 37

• Parallel sheets of aluminosilicates.
• The surface of these sheets contain hydrated hydroxyl groups.

Question 38

What does high soil acidity affect?

Answer 38

• Rate of pant growth
• Cation exchange process
• The action of bacteria in the soil.

Question 39

Why is a decreased pH good for soil?

Answer 39

• Decreased pH means lots of hydrogen ions. Increased concentration will push equilibrium to the right to displace cations into aqueous form to be taken up by the plant.

H+(aq) + Ca2+(soil) <—–> H+(clay) + Ca2+(aq)

Question 40

What happens if there is increased rainfall for plants with soil salinity?

Answer 40

Increased rainfall will wash away all the nutrients in aqueous form being taken up by the plant. This leads to lack of nutrients for the plants and can lead to plant death.

Question 41

What happens if aluminum ions are released into soil?

Answer 41

• They are toxic to plants.

Question 42

Define soil salinity.

Answer 42

The measure of concentration of soluble salts in soil.

Question 43

Why is high soil salinity bad?

Answer 43

• It means there is increased concentration of salts outside the plant, so the plant won’t be taking up water, it will be expelling it via osmosis. This means that the plant is not taking up water with the required nutrients, which is bad for the plant.

Question 44

Calcium ions flocculate clay particles together in soils. Describe the consequence of dryland salinity on soil structure.

Answer 44

• Soil contains clay sheets held together through secondary interactions between water and cations.
• Na+ is larger, and less positively charged than calcium, therefore is less strongly attracted to the negative clay particles, weaking the attraction force between the layers of clay. This leads to soil dispersion which weakens aggregates in the soil and leading to a structural collapse. This means that the soil is susceptible to breaking because Na+ does not flocculate clay well, causing cracks in the soil.