Bond Enthalpies.

But first, just to recap.

Enthalpy of Combustion; The enthalpy change it takes to burn one mole of compound in oxygen under standard conditions, all products/reactants in their standard states.

Enthalpy of Formation; The enthalpy change it takes to form one mole of compund from its constituent elements, under standard conditions, all products/reactants in standard states.

(I can finally remember these without looking. YEA! :D)

So yea, bond enthalpies.

Energy has to be put in to break a bond, endothermic. (takes in heat.) Bond Dissasociation energy is the value of energy required to break a covalent bond, with all species in a gassious state. And in reverse, the same amount of energy would be given out, exothermically. (When it is formed)

Each bond may have slightly different enthalpies in different molecules. Becuase of this, bond enthalpies are normally averages, to make things a bit of accurate. However, using them for calulations, answers won't be entirely accurate, as I'm sure you can tell, but they are quicker to use.

We can use bond enthalpies to work out the enthalpy changes in reactions. We do this by counting up the types of bonds, and how many there are, and filling in their average values. All the bonds have to break, in the reactants, so add these up to get the energy that must be put in. The energy given out is the added up reactants. The difference between these two values is the enthalpy change. Also, if more energy is given out then put in, it is exothermic and needs a '-' sign at the start.

Although, a way to shorten it down is to only calculate with the bonds that actually take part in the reaction, as this will really cut down calculation times.

In a lot of past exam questions I've seen recently there's a load of stuff about comparing the average bond enthapies to thermodynamic type things. This would be that, in a thermodynamic cycle, all the calculated (delta)Hf/c values are used of the actual compounds, whereas with bond enthalpies they are average, so thermos are more accurate.

Thermochemical Cycle things. ΔHf, ΔHc

Hess' Law states that the enthalpy change for a chemical reaction is the same, whatever ther route taken for the reactants to products. This means they can be made into cycles.

When in enthalpy of formation, (the enthalpy it takes to form one mole of compund from its constituent elements, under standard conditions, all reactants/products in standrad states), you write the balanced equation of your reactions on top, and the constiuent elements on the bottom. The arrows point up. Then, to follow the path of it, fill in the values, and flip the first arrow, and the negative/positive charges round. Add it up and you'll get the ΔH, from the ΔHf.

When it's the enthalpy of combustion, (the enthalpy it takes to burn one mole of compound in oxygen under standard conditions, with all products and reactants in their standard states), the balanced equation is on the top, and the arrows point downards. You'd the flip the second arrow and charges when you add all stuffs upppp.

So,

• Write an equation for the reaction
• Write down the constituent elements or CO2 and H2O at the bottom, balanced.
  
• Put in all the ΔHf/ΔHc values you have.
  
• Turn the correct arrows around
  
• Follow the path round, adding up.
  

Chem bits. Kinetics and that (:

Endothermic, heat going in. Exothermic, heat given out. (In reaction.)

So, endothermic, as in, takes heat/energy in to make the reaction actually go anywhere. In exothermic, it gives out energy as heat.

Enthalpy change is when we measure heat change at a constant pressure.

Enthalpy is shown by the letter H, and change is shown by Δ/delta. So, a change in is enthalpy is ΔH.

Enthalpy level diagrams show the relative enthalpy levels of the reactants, and products, which, in turn, shows the ethalpy change.

Enthalpy of formation is the enthalpy change when one mole of compund is formed from it's constituent elements, under standard conditions, all reactants and products in standard states.

Enthalpy of combustion is the enthalpy change when one mole of compound is burned in oxygen under standard conditions, all products and reactants in standard states.

Enthalpy change = mass of substance X specific heat capacity X change in temperature.

OR

q=mcΔT

(Q = enthalpy change)

In a calorimeter, fuel is burnt to heat a known mass of water (m), and then measure the temperature at the beginning and throughout, to get the change in temperature (ΔT) and the standard heat capacity can be used, or one is given, and then q=mcΔT can be used.

The calorimeter, and measurement of enthalpy change can be made more accurate by preventing heat loss. This can be as simple as adding a lid, draught screen, and insulation around the beaker.

To measure enthalpy changes in solution it is normally in a polythene cup. These are insulators, so heat loss will be reduced, and the heat capapcity is low, and this means they don't absorb much heat, and it all stays in the solution.

Chlorine and all that jazz (:

What is chlorine used for?

• properties
• oxidisng abilities.
  

Chlorine is used in water to kill off unwanted bacteria.

Cl2(g) + H2O(l) => HClO(aq) + HCl(aq)

This ONLY happens in the sun/UV

Chlorine = swimming pool outdoors = pH change.

reaction w/ alkali ...
Cl2 + 2NaOH => NaClO + NaCl + H2O

Sodium chloride = bleach.

The agents, oxidisng and reducing, are the opposite of what happens.

Group Seven :D

Trends:

1. Electronegativity. This increases as you go up the group.
   
2. Atomic Radius, increases as you go down the group.
   
3. Melting point, increases as you go down the group.
4. Boiling point, increases as you go down the group.
   
5. The oxidisng agent ability increases and you go up the group (so, Astetine to Fluorine.)

Their colours, in solution... Fluorine is clear, Cl is yellowy, Br is red/brown, and Iodene is purple.

The Sodium Hallides + Sulphuric Acid:

Eqn1 ...
NaCl (solid) + H2SO4 (liquid) => NaHSO4 (solid) + HCl (gas)
This produces steamy fumes of HCl

Eqn2 ...
- NaBr(s) + H2SO4(l) => NaSO4(s) + HBr(g) [Steamy fumes]
-- 2H+ + 2Br- + H2SO4 => SO2 (g) +2H2O(l) + Br(l) [Brown fumes]


Eqn3 ...
- NaI(s) + H2SO4(l) => NaH2SO4(s) + HI(g) [Steamy fumesof HI]
-- 2H+ + 2I- + H2SO4(aq) => H2S(g) + 4H2O(l) + I2(s) [Black solid forms, (I2), bad egg smell.]

Group Two Metals

Trends that are needed to know:

1. The solubilities of group two Hydroxides increase as you go up the group (Radium to Beryllium)
2. The solubilities of Group two Sulphate decrease as you go down the group (Beryllium to Radium)
   

Group two are all metallic and therefore, have high melting points. The sea of delocalised electrons are further from the nuclei as you go down the group, and therefore, the strength of the bond decreases and the melting point decreases.

Haemoglobin

Is a protein consisting of:

• 4 Polypeptide chains
• These are coiled into a helix
• Which is folded into a specific shape
  
• These are linked to form a spherical molecule.
  

Each polypeptide is associated with a haem group, containing and Fe2+ ion.

Ferrous (Fe2+)attaches to the middle of the heam group.

Hb+ 4O2 = HbO8
or
Haemoglobin + Oxygen = Oxyhaemoglobin

Has to associate/load with oxygen in the lungs. High affinity. Disociates at the tissues that require it.

Carbon Dioxide makes a weak acid when in water (solution), this changes the pH, and therefore, the shape of the protein, (temporarily.)

Why can haemoglobin unload? :

• Low partial pressure of O2 means the oxygen is used in aerobic respiration, which means there is a higher CO2 concentration.
  
• This reduces the pH (as CO2 is acidic in solution)
  
• Haemoglobin changes it's shape in high CO2 concentrations.
  
• This means it binds to the oxygen more loosely.
  
• And can, therefore, unload where needed.
  

Erythrocytes- Red Blood Cells
Leucocytes- White Blood Cells.

Plasma % in blood is important, makes it fluid, and flows easier.

Adaptations of a red blood cell:

• Small size (7 micrometres.)
  
• Flattened biconcave disc shape.
• Thin central section
• Absence of organelles.
  
• Filled with haemoglobin

Oxygen dissasociation curve: Shows how much oxygen is combined with Hb at different concentrations of oxygen.

Haemoglobin is never 100% saturated.

Pp of oxygen is lower in lungs due to presence of CO2 and water vapour so it would be less.

Thoughts?
-Nin.

Tissue fluid, etc. :D

Tissue fluid carries oxygen to cells, takes waste products. Important substance.

What is tissue fluid?

• formed from blood plasma, leaking out of the capillaries.
• Is a watery liquid that contains glucose, amino acids, fatty acids, salts and oxygen. Tissue fluid supplies all these substances to the tissues and also recieves waste materials, for example, carbon dioxide from the tissues.
• Is the means by which materials are exchanged between the blood and cells of the body
• It provides a very constant environment for cells.

Lymphatic system starts in capillaries, series of tubes, join to make bigger lymph nodes.

Formation of tissue fluid and return to circulatory system:

• Blood leaving heart passes along arteries, narrower arterioles, and then even narrower capillaries.
• This creates a pressure called hydrostatic pressure at the arterial end of the capillaries
• Hydrostatic pressure forces fluid (and plasma) out.
• This is opposed by the hydrostatic pressure of the tissue fluid outside, and the lower water potenital in the due to the plasma proteins that pulls water back into the arteries.

Thoughts?

-Nin.

Transport systems and stuff.

Why do some organisms need a transport system?

• Large organism: Small surface area to volume ratio, needs can't be met by the surfaace of the body.
  
• Diffusion is inadequate over large distances.
  
• Transport system required to take materials from cells to exchange surface and vice versa.

The lower the SA/V ratio, and the more active the organism, the greater the need for a specialised system with a pump.

Main function of a blood system is to transport substances around the body. Allows organism to move substances around in bulk, quickly, over large distances. Blood vessels, a closed system of tubular vessels contain blood and transport it. The heart is the mechanism that pumps. Valves maintain this flow in one direction.

Arteries take blood away from the heart into ARTERIOLES, thinner branches of arteries in organs. CAPILLARIES- mass of very narrow vessels which penetrate tissues. Link ARTERIOLES to VENULES. VENULES, blood flows back from capillaries into veins, which transports blood back to the heart.

Structure of blood vessels:
Arteries, arterioles, and veins have the same basic layered structure. Relative proportions of each layer differ between each type of blood vessel:-

• Tough outer layer- resists pressure changes, inside and out, (OUTER LAYER)
  
• Muscle layer, can contract and control the flow of blood.
  
• Elastic layer, helps maintain pressure by stretching and recoiling.
  
• Endothelium- thin inner lining, smooth to prevent friction, and thin to allow diffusion. INNER LAYER.
  
• Lumen - central cavity of blood vessel.
  

Have different proportions of these features in different types.

Arteries- thick walls to maintain pressure, thin to absorb it and keep it constant.

Arteries Have a smooth endothelium, inner layer, cells are flat. This ensures the blood flows freely and doesn't stick to the walls. It has a layer of elastic fibresm, which allows it to expandand recoil each time the heart beats, smoothing out pressure changes. The have a realtively thick muscle layer, so that smaller arteries can be constricted to control the volume of blood passing through them. There is a tought outer layer of protein fibres, which allows the wall to resist bursting under pressure.

Arteriole's muscle layers are relatively thicker then that of the arteries. This allows contraction of the muscle allowing constriction of the lumen of the arteriole, restricting bloodflow and controlling it. Also the elastic layer is thinner then that in the arteries, as the blood pressure is lower.

Veins have a realtively thin muscle layer, as they carry blood away from the tissues, and therefore, cannot control blood flow to the tissues. The elastic layer is thin, becuase there is a low blood pressure, and the recoil action cannot be made. The walls are thinner then the arteries walls are. This is because blood pressure is lower and pressure is resisted less. There are valves throughout (the body muscles contract and compress them), this ensures that blood flows one way.

Capillaries are one cell thick, and their function is to exchange metabolic material. The flow of blood is slow in capillaries, which allows more time for exchange of materials. Also, the walls are extremely thin, which makes for a short diffusion distance. There are numerous capillaries, which provides a large SA for diffusion. They are narrow in diameter, so they can penetrate tissues.

Potometer , other random notes about fish and that.

Potometer:

It is difficult to measure transpiration, because it is difficult to collect and condense, and you can't measure vapour.

A leafy shoot would be cut under water, because otherwise, an air bubble would go into the xylem, breaking the transpiration stream, and stopping the movement up the shoot. If it is in water, water will be drawn in instead, and the column maintained.

The syringe in a potometer is to refill the capillary tube when the bubble reaches the stem so water can continue to be measured.

Assumption made if potometer is used to measure the rate of transpiration - all water taken up is being transpired.

Small organisms have a sufficient gas exchange system as the have a large sa/v ratio.

Large animals have blood systems because with a large animal, gas exchange diffusion distance to cells would be too far, so, blood system is needed for rapid oxygen supply.

Small fish, no gill, because exchange/diffusion can take place through body surface, as they have a high surface area to volume ratio and a short diffusion distance.

Mackerel swim faster then toadfish => Mackerel have thinner lamellae, short diffusion distance, rate of gas exchange is quicker, get oxygen for respiration faster, to release ATP for muscle contraction.

Gill makes oxygen efficient => Thin lamellae, short diffusion distance to blood capilaries

Counter current flow maintains a concentration gradient, doesn't reach an equilibrium, takes place along whole gill.