I. Molecular dynamics theory

1, the object is composed of a large number of molecules.

Microscopic quantities: molecular volume V 0, molecular diameter d, molecular mass m 0

Macro quantities: material volume v, molar volume V A, object mass m, molar mass m, and material density ρ.

Connecting bridge: Avon Gardello constant (N A = 6.02×10mol) ρ = 23-1mm = V A.

(1) Molecular mass: m 0 = ρ V A M V A M = = V = = (2) Molecular volume: 0 N A N 0n N A N A N A N A N A N A P N A.

(For gas, V 0 should be the space occupied by gas molecules)

(3) Molecular size: (order of magnitude 10- 10m)

1 sphere model. V0 = ○ 6V VaM4d = = π () 3 Diameter d =0 (this model is generally used for solids and liquids) N A ρN A 32π.

V s- the area of monomolecular oil film, v- the volume of pure oleic acid dropped into water. Estimation of molecular size by s oil film method: d =

2 cubic model. D = ○ 0 (this model is generally used for gases; For gases, d should be understood as the average distance between adjacent molecules.) Note: Solid and liquid molecules can estimate the molecular mass and size (molecules are considered to be closely arranged one after another);

The distance between gas molecules is so large that the size can be ignored and it is impossible to estimate the size. Only the space and molecular mass occupied by gas molecules can be estimated.

(4) number of molecules: n = NNA = mρ v ρ v nA = nA or N =nN A =N A =N A M M V A M

2. Molecules never stop moving randomly.

(1) Diffusion phenomenon: the phenomenon that different substances enter each other. The higher the temperature, the faster the diffusion. It directly shows that the molecules that make up an object always move irregularly, and the higher the temperature, the more intense the molecular movement.

(2) Brownian motion: the irregular motion of solid particles suspended in liquid.

The reason is that solid particles are impacted irregularly by liquid molecules around the particles, which indirectly indicates that liquid molecules are constantly moving irregularly.

1 Brownian motion is the motion of solid particles rather than the random motion of molecules in solid particles.

Brownian motion reflects the irregular motion of liquid molecules, not the motion of liquid molecules.

The Brownian motion path shown in the textbook is not the trajectory of solid particles.

④ The smaller the particles, the more obvious Brownian motion; The higher the temperature, the more obvious Brownian motion.

There is attraction and repulsion between molecules.

① The intermolecular attraction and repulsion must exist at the same time, and both decrease with the increase of intermolecular distance.

It increases with the decrease of intermolecular distance, but the repulsive force changes rapidly, and the actual molecular force is 0.

The resultant force of molecular repulsion and molecular attraction.

② For the expression and change of molecular force, we should pay attention to two distances for the curve, namely the equilibrium distance r 0 (about 10- 10 m) and 10r 0.

(i) When the intermolecular distance is r 0, the attraction is equal to the repulsion, and the molecular force is zero.

(ii) When the molecular spacing r > r 0, the attraction force is greater than the repulsion force, and the molecular force shows the attraction force. When the intermolecular distance changes from r 0,

When it increases, the molecular force increases first.

After the big reduction.

(iii) When the molecular spacing r < r 0, the repulsive force is greater than gravity, and the molecular force is repulsive. When the intermolecular distance decreases from r 0, the molecular force increases continuously.

Second, temperature and internal energy.

1, statistical law: the movement of a single molecule is irregular and accidental; The collective behavior of a large number of molecules is governed by statistical laws. The velocity of most molecules is around a certain value, which satisfies the distribution law of "more in the middle and less at both ends".

2. Average kinetic energy of molecules: the average of all kinetic energy of molecules in an object.

① Temperature is a sign of average kinetic energy of molecules.

② At the same temperature, the molecular average kinetic energy of any object is equal, but the average velocity is generally different (molecular mass is different).

3. Molecular potential energy (1) generally stipulates that the molecular potential energy at infinity is zero.

(2) The molecular potential energy of the molecular force doing positive work decreases, while the molecular potential energy of the molecular force doing negative work increases. (3) Relationship between molecular potential energy and intermolecular distance r 0 (analogy elastic potential energy) ① When r > r 0, r increases, molecular force is gravity, and molecular potential energy increases when molecular force does negative work.

② When R > R 0, R decreases, molecular forces repel, and molecular potential energy of molecular forces doing negative work increases.

③ When r =r 0 (equilibrium distance), the molecular potential energy is the smallest (negative value).

(4) Factors determining molecular potential energy:

Macroscopically, molecular potential energy is related to the volume of an object. (Note that the molecular potential energy does not necessarily increase with the increase of volume. )

Microscopically, molecular potential energy is related to intermolecular distance r.

4. Internal energy: the sum of kinetic energy and molecular potential energy of all molecules in an object. E = N E K+E P。

(1) internal energy is a state quantity. (2) Internal energy is a macroscopic quantity, which is meaningful only for objects composed of a large number of molecules, but not for a single molecule.

(3) The internal energy of an object is determined by the amount of matter (number of molecules), temperature (average kinetic energy of molecules) and volume (intermolecular potential energy), and has nothing to do with the macroscopic mechanical motion state of the object. There is no necessary connection between internal energy and mechanical energy.

Third, thermodynamics and the law of conservation of energy.

1. Two ways to change the internal energy of an object: doing work and heat transfer.

Equivalent heterogeneity: Doing work is the conversion of internal energy and other forms of energy; Heat transfer is the transfer of internal energy between different objects (or different parts of the same object), and their effects of changing internal energy are the same.

② Conceptual differences: temperature and internal energy are state quantities, while heat and work are process quantities. The premise of heat transfer is temperature difference, which transfers heat instead of temperature, and is essentially the transfer of internal energy.

2, the first law of thermodynamics

(1) Content: Generally, if an object does work and transfers heat with the outside, the sum of the work W done by the outside to the object and the heat Q absorbed by the object from the outside is equal to the increase of the internal energy of the object. The mathematical expression is: δ u = w+q.

(3) Symbolic law:

(4) adiabatic process q = 0, key words "adiabatic substance" or "rapid change"

(5) For an ideal gas (without considering the intermolecular interaction, the internal energy is only determined by the temperature and the total number of molecules, and has nothing to do with the gas volume. ① δ u depends on the temperature change, and the temperature increases δ u >; 0, the temperature drops by δ u.

②W depends on the volume change. When v increases, the gas does external work, w0;

③ Special case: if gas diffuses into vacuum, w = 0.

3, the law of conservation of energy:

(1) Energy will neither be generated out of thin air nor disappear out of thin air. It can only be transformed from one form to another, or transferred from one object to another, and its total amount remains unchanged during the transformation or transfer. This is the law of conservation of energy.

(2) The first perpetual motion machine: a machine that does not consume any energy and can continuously do external work. (violating the law of conservation of energy)

4, the second law of thermodynamics

(1) Directionality of heat conduction: The process of heat conduction can be spontaneously carried out from a high-temperature object to a low-temperature object, but it cannot be spontaneously carried out in the opposite direction, that is, heat conduction has directionality and is an irreversible process.

(2) Description: ① Spontaneous process is a natural process without external interference.

(2) Heat can be spontaneously transferred from a high-temperature object to a low-temperature object, but heat cannot be spontaneously transferred from a low-temperature object to a high-temperature object.

(3) When heat can be transferred from a low-temperature object to a high-temperature object, there must be "external influence or help", that is, it can only be done by external work.

(3) Two expressions of the second law of thermodynamics

Clausius stated that it is impossible to transfer heat from a low-temperature object to a high-temperature object without causing other changes.

(2) Kelvin states that it is impossible to absorb heat from a single heat source and make it completely useful without causing other changes.

(4) Heat engine

A heat engine is a device that converts internal energy into mechanical energy. Its principle is that the heat engine absorbs heat Q 1 from the high-temperature heat source, pushes the piston to do work w, and then releases heat Q 2 to the low-temperature heat source (condenser). (Working conditions: two heat sources are required)

② According to the law of conservation of energy, we can get: Q 1=W+Q2.

③ We call the ratio of the work done by a heat engine to the heat absorbed from a heat source as the heat engine efficiency, which is expressed by η, that is, η= W/Q 1.

(4) The heat engine efficiency can't reach 100%.

(5) The second perpetual motion machine (①) is supposed to absorb heat from a single heat source without causing other changes and become a useful heat engine. (2) the second perpetual motion machine can't do it, and it doesn't violate the first law of thermodynamics or the law of conservation of energy, and it violates the second law of thermodynamics. Reason: Although mechanical energy can be completely converted into internal energy, internal energy cannot be completely converted into mechanical energy without causing other changes; The conversion process between mechanical energy and internal energy is directional.

(6) Universality: The macroscopic process related to thermal phenomena is irreversible. For example; Diffusion, gas expansion to vacuum, energy dissipation.

(7) Entropy and entropy increasing principle

① Microscopic significance of the second law of thermodynamics: all natural processes always proceed in the direction of increasing disorder of molecular thermal motion.

② Entropy: a physical quantity to measure the disorder degree of the system. The more chaotic the system is, the higher the disorder degree is and the greater the entropy value is.

③ Entropy increasing principle: In an isolated system, all irreversible processes are bound to develop in the direction of entropy increasing. The second law of thermodynamics is also called the principle of entropy increase.

(8) Decline of energy: With the increase of entropy, all irreversible processes always make energy gradually lose its ability to do work, from available state to unavailable state, and the quality of energy becomes worse. Another explanation: in the process of energy conversion, the disorder degree of molecules increases with the generation of internal energy.

At the same time, the internal energy can be dissipated into the surrounding environment and cannot be reused.

Collect it for use) 4. Solid and liquid 1, crystal and amorphous ① particle arrangement inside the crystal.

It is regular and periodic in space, so the number of particles at the same distance in different directions is different, which makes the physical properties different (anisotropy). Because polycrystalline is composed of many small crystals (single crystals) arranged in disorder, it does not show anisotropy and its shape is irregular.

② When the crystal reaches the melting point, it changes from solid to liquid, and the intermolecular distance will increase. At this time, the crystal will absorb heat from the outside to destroy the crystal lattice structure, so the heat absorption is only to overcome the attraction between molecules and only to increase the potential energy of molecules. The average kinetic energy of molecules remains unchanged, and the temperature remains unchanged.

2. Liquid crystal: a special state of matter between solid and liquid.

Physical properties ① It has the optical anisotropy of crystal-its molecules are arranged in a certain direction.

② Liquidity-On the other hand, the arrangement of molecules is disordered.

3. Surface tension phenomenon and capillary phenomenon of liquid.

(1) Surface tension ── The molecules in the surface layer (thin liquid layer in contact with gas) are sparse, r > r 0, and the molecular force shows attraction. Under the action of this force, the liquid surface tends to shrink to the minimum, and this force is the surface tension. The direction of surface tension is tangent to the liquid level and perpendicular to the dividing line of this part of the liquid level.

(2) Permeability and non-permeability phenomena:

(3) Capillary phenomenon: For the tube wall of a certain liquid or material, the thinner the inner diameter of the tube, the more obvious the capillary phenomenon.

① The thinner the inner diameter of the pipeline, the higher the liquid; ② loose soil destroys capillaries and preserves groundwater; Compacting the soil, thinning the capillaries and sucking up the water.

Five, the ideal gas gas experiment law

(1) In order to explore the relationship among pressure p, volume v and temperature t of an ideal gas with a certain mass, the control variable method is adopted.

(2) Three kinds of changes: ① isothermal change, Boyle's law: PV = C2 isovolumetric change, and Charlie's law: P/T = C.

③ Constant pressure change, Gay-Lussac's law: V/T = C.

O isothermal change t 1 < T2O isovolumic change v 1 < V2O isobaric change p 1 < P 2 tips:

① The figure in isothermal change is a branch of hyperbola, and the figure in constant volume (pressure) change is a straight line passing through the origin (the dotted line near the origin indicates that the temperature is too low and no longer satisfies the law).

(2) The double lines in the figure show the graphs of the same gas in different states, and the dotted lines show two methods to judge the state relationship.

(3) For the change of constant volume (pressure), if the physical quantity on the horizontal axis is temperature t, the coordinate of the intersection point is -273.8+05.

(3) Equation of state of ideal gas

Pv p 1V 1p 2V 2= constant) Pv

=nRT (n is the number of moles) = For a certain quality of ideal gas, there are

(or T T 1T 2.

(4) Microscopic explanation of gas pressure: A large number of gas molecules frequently collide with the wall. The pressure is related to the number of collisions of gas molecules on the wall in unit time and unit area. Determinants: ① The average kinetic energy of gas molecules is macroscopically determined by the temperature of gas; ② The number of molecules per unit volume (molecular density) is macroscopically determined by the volume of gas.

Six, saturated steam and water vapor saturation pressure.

1, saturation pressure of saturated steam and water vapor:

The number of molecules returning to the liquid per unit time is equal to the number of molecules flying out of the liquid surface. At this time, the density of steam no longer increases, and the liquid no longer decreases. Liquid and vapor will reach equilibrium, which is called dynamic equilibrium. We call vapor in dynamic equilibrium with liquid saturated vapor and unsaturated vapor unsaturated vapor. At a certain temperature, the pressure of saturated steam is constant, which is called water vapor saturation pressure. The pressure of unsaturated steam is less than the saturation pressure of water vapor.

Influencing factors of water vapor saturation pressure: ① It is related to temperature. With the increase of temperature, the saturated air pressure increases.

② The saturated pressure of steam has nothing to do with the volume of saturated steam.

3) Humidity of air (1) Absolute humidity of air: The humidity expressed by the pressure of water vapor contained in air is called absolute humidity of air.

(2) Relative humidity of air: Relative humidity = actual steam pressure of water vapor and saturated pressure of water vapor at the same temperature.

Relative humidity can better describe the humidity degree of air, and affect the evaporation rate and people's feeling of dryness and wetness.

(3) Wet and dry bubble hygrometer: The greater the difference between the two thermometers, the smaller the relative humidity of the air.