5)Fuel value of food Calorie content of food.

All products (sugar, proteins, carbohydrates) oxidizing in organism split up into simple material. Heat of oxidation or combustion it is calorie content of food. Each product has its own value of energy. Energy value or calorie content of food is heat amount evolved by complete oxidation of 100 grams of product.

Proteins, fat, carbohydrate: the sum of energy of these compounds makes the whole value of heat evolved during oxidation of these products in an organism.

Calorie coefficient (q) or calorie content it is amount of energy in kcal evolved during the oxidation of 1 gram of proteins, fat, carbohydrate.

So proteins' calorie coefficient (q)

Proteins 4 kcal/gm

Fat 9 kcal/gm

Carbohydrates 4 kcal/gm

1 kcal-4.18 kJ

Q general = Q proteins + Q fat + Q carbohydrates

Q proteins = m proteins (grams) * q = m proteins * 4, where q is a calorie coefficient.

Adult needs 2200 - 2800 kcal per day ( 24 hours )

6) Standard condition and thermochemical (enthalpy of formation)

T=298 K (25)

P = 1.01. x 105 kpa ( 1 atmosphere ) Pascal

N = 1 mole, n - number of molecules.

Standard heat of some reactions are given in standard table charts.

Thermo-chemical equation.

A chemical equation which gives the physical states of both reactants and products along with the amount of heat evolved or absorbed during the process is called thermo-chemical equation.

C(solid) + O2 (gas) <---> CO2 (gas) - 396 kJ

∆H = -396kJ

sometimes they use abbreviation 1 - liquid

s – solid

g - gas

∆H is heat absorbed or evolved during the chemical reaction at constant temperature and constant pressure.

7) Second law of thermodynamics. Spontaneous and non spontaneous processes . Gibb's energy. Entropy.

The second law of thermodynamics

In thermodynamics all the processes are reversible and irreversible.

The main processes in organism are irreversible.

Organisms getting older and the other irreversible changes in nature.

Reversible is a process in which thermodynamic system and surroundings are able to turn to a primary state without any changes in both system and the surroundings.

Irreversible is a process in which thermodynamic system transforms from one state to another and the new system does not change back to the primary state. Thus reversible process is not possible neither in system nor in surroundings.

Equilibrium state is a state when the properties of a system do not change for a long time.

The Second Law of Thermodynamics is about spontaneous processes take place with disorder of a system increasing.

Entropy is the main characteristic of system's disorder.

Entropy is a property of a system which shows the disorder of a system or randomness in the system. So entropy is degree of system's disorder.

It is denoted by the symbol of entropy - S [ J/K * mole]. The entropy of a perfect crystal at 0 K is arbitrarily taken as zero. The crystalline state is considered to be perfectly ordered state at absolute zero. With the rise in temperature on heating, molecular motion sets in (KE∞T) and the entropy (disorder) starts increasing. Thus, entropy increases from solid to liquid to gas. The change in entropy (S_final - S_initial) is denoted by ∆S and is given by:

∆S = S_final - S_initial

or ∆S = S_products - S_reactants

If the entropy increases in a process, ∆S is given a positive sing. If it decreases, ∆S is given a negative sing.

So spontaneous processes take place with entropy increasing.

There are different definitions of Second Thermodynamic Law.

Clausius's definition: “The heat cannot spontaneously transfer from cold body to hot body.”

Carno's definition: “The heat is unable to transform into work completely. Part of this energy is spent for heating up the environment.”

D = A/Q where A - useful work which makes from absorbing heat, Q - heat at the expense of heater.

(This is coefficient of efficiency of imaginary machine)

This formula is one of the mathematical expression of Second Law.

Gibbs energy. ∆H = G + E , where G - Gibbs's energy which is also called free energy at the expense which the useful work is fulfilled.

E - is bonded energy. This energy is not free and it is impossible to fulfill any useful work at the expense of this energy.

S*T we can sign bonded energy ( entropy and temperature ) spent for internal energy of a system change. According to this expression we can write the general formula.

Free energy of a system is a measure of its capacity to do useful work.

G = H – TS = E + PV – TS

∆G = ∆E+∆(PV) - ∆ (TS)

For a change taking place at constant temperature and pressure:

∆(PV) = P∆V and ∆(TS) = T∆S

∆G = ∆E+ P∆V - T∆S or

∆G =∆H - T∆S

This equation is known as Gibbs-Helmoholtz equation.

∆H heat of a system = ∆G + ∆S*T

This is united Law of Thermodynamics. 1^st and 2^nd law of thermodynamics.

∆G - useful work is fulfilled at the expense of this energy. This is free Gibbs's energy.

∆S*T – degree of systems by definite temperature.

Some examples:

Solid – liquid – gas in this sequence entropy increases because of aggregate state change. AS > 0

CaCO₃ (s) -> CaO (s) + CO₂ (g), ∆S > 0, entropy increases because of number of particles increasing.

2H₂ (g) + 0₂ (g) -» 2H₂0 (g) , ∆S < 0

∆H heat of a system = ∆G + ∆ST or ∆G - ∆H - ∆S*T

1. ∆G <0 negative

such processes go on spontaneously. It is chemical change in which spontaneous forward process is possible.

2. ∆G>0 positive

Backward spontaneous reaction is possible.

3. ∆G = 0

Thermodynamic equilibrium state.

Living organism is heterogeneous, polyphase, polycomponent, open system. Organism exchanges both energy and matter with the surroundings.