高考化学个考点精讲 考点 化学反应中的能量变化（College entrance examination chemistrytest sites, precise test sitechemical reaction in the energy change）

1、高考化学58个考点精讲 考点3 化学反应中的能量变化（College entrance examination chemistry 58 test sites, precise test site 3 chemical reaction in the energy change）Test site 3 energy change in chemical reactions1. review the key pointsUnderstand the change in energy in a chemical reactionUnderstanding exothermic reactions,

2、 endothermic reactionsUnderstand the reaction heat, combustion heat and heat, and the heat equation of writing2. difficulties focusI. heat of reaction1. The amount of heat released or absorbed during a chemical reaction, usually called reaction heat. The reaction heat is indicated by the symbol Delt

3、a H, and the unit is usually kJ/mol. When H is negative, it is exothermic; when H is positive, it is endothermic reaction. An instrument for measuring the heat of reaction is called a calorimeter.2. Combustion heat: at 101kPa, when the substance 1mol is completely burned, the heat released from the

4、stable oxide is called the burning heat of the substance.3, neutralization heat: in dilute solution, the acid and alkali neutralization reaction to produce 1molH2O, at this time the reaction heat called neutralization heat. The middle school stage mainly deals with the reactions of strong acids and

5、strong bases.Two thermochemical equation1, the writing heat response equation should pay attention to the problem:(1) because the value of the reaction heat is related to the temperature and pressure of the reaction, it must be noted that "101kPa" and "25" are not indicated.(2) t

6、he aggregation state of matter is different, the numerical value of reaction heat is different, so the aggregation state of matter should be indicated.(3) the stoichiometric quantity in a thermochemical equation is the quantity of a substance of the corresponding substance. It can be either an integ

7、er or a fraction.2, write the general steps of thermochemical equations(1) write the chemical equation indicating the aggregated state according to relevant information and trim.(2) according to the stoichiometric number of each substance in the chemical equation, the corresponding numerical value o

8、f the reaction heat is calculated.(3) if the exothermic reaction is negative, the delta H is negative, and if the endothermic reaction is positive, the delta H is positive. And write in the first step of the equation behind, in the middle with ".".(4) if the subject otherwise requires, suc

9、h as the thermochemical equation of the combustion heat of the fuel and the thermochemical equation about the neutralization heat, the stoichiometric number of the thermochemical equation can be converted into fractions.Three. Determination of neutralization heat1 、 preparation before determination(

10、1) select the accurate thermometer (accurate to 0.10C) and proofread (the temperature requirement is accurate to 0.10C).(2) use a thermometer to light. A thermometer that has just been measuring high temperature does not flush with water so as not to burst.(3) to measure the temperature of the solut

11、ion, the thermometer should be hung so that the mercury sphere is in the middle of the solution. Do not lean on the beaker wall or plug into the bottom of the beaker. Thermometer shall not be used as a stirring stick.2, in order to improve the accuracy of neutralization heat measurement, some proble

12、ms should be paid attention to during the experiment(1) as an instrument and device of a calorimeter, the effect of heat preservation and insulation must be better. Therefore, you can use the thermos cup to do. If the method is used in the textbook, make sure that the beaker of small beaker is flat

13、with the beaker cup so that the heat loss can be reduced.(2) the concentration of hydrochloric acid and sodium hydroxide solution should be accurately prepared, and the concentration of sodium hydroxide solution should be slightly larger than the concentration of hydrochloric acid. In order to make

14、the neutralization heat more accurate, the concentration of hydrochloric acid and sodium hydroxide solution should be small and not big enough.(3) the bulb of the thermometer must be completely immersed in the solution and read again after a period of time to improve the accuracy of the measured tem

15、perature.(4) the operation should be done quickly in order to minimize the loss of heat.(5) in order to reduce the experimental error, repeat the experiment 23 times, and the data is averaged.Note: a comparison of the size of the reaction heat, reaction heat: comparison of the size, usually in diffe

16、rent conditions (temperature, pressure, material aggregation etc.) with a chemical reaction, or in the same conditions (temperature and pressure) were similar between the chemical reaction under. When compared to the good from the difference, grasp its essence, so as to solve problems. The main fact

17、ors affecting the size of the reaction heat are the following aspects.1. Stoichiometry in thermochemical equations.Such as 2mol, hydrogen combustion heat release under the same conditions, 1mol hydrogen combustion when released 2 times.2 the aggregation or crystalline structure of matter. If the sam

18、e amount of hydrogen burns to produce liquid water, the amount of heat released is greater than that produced by gaseous water.3, the strength of the chemical bond. When the hydrogen halides of 2mol are generated by the reactions of single elements, the amount of heat released in HF, HCl, HBr and HI

19、 is reduced accordingly.Two. The application of Gass's law and the calculation of combustion heat and neutralization heatThe magnitude of the reaction heat in chemical reactions is related to the kind, amount and aggregation state of reactants, products, and the reaction pathways. According to t

20、he law of conservation of energy, no matter whether the reaction is completed in one step or completed in several steps, the heat of reaction is a definite value as long as the starting state and the ending state of the reaction are determined. This is the famous Gass's law.3. examples elaborate

21、case 1 known at 25 degrees C, 101kPa, lgC8H18 (octane) combustion, the formation of carbon dioxide and liquid water, 48.40kJ heat release. The thermochemical equation describing the above reaction is correct ()A.C8H18 (1) 22.5O2 (g) = 8CO2 (g) 9H2O (g); H = 48.40kJ - Mol1B.C8H18 (1) 22.5O2 (g) = 8CO

22、2 (g) 9H2O (1); H = 5518kJ - Mol1C.C8H18 (1) 22.5O2 (g) = 8CO2 (g) 9H2O (1); H = 5518kJ - Mol1D.C8H18 (1) 22.5O2 (g) = 8CO2 (g) 9H2O (1); H = 48.40kJ - Mol1analysis according to the subject conditions, the generated water is liquid, so the A is wrong, and the 1gC8H18 emits heat after burning 48.40kJ

23、, so the 1molC8H18 is completely burnt and emits heat 5518kJ, and the heat release is expressed by "-", so C is wrong.answer Banalysis the writing of thermochemical equation is difficult. It is important to pay attention to the relation between the coefficient and the reactant in the proce

24、ss of writing.keyword the writing of reaction heat and thermochemical equation2 in the same temperature and pressure, the following was Q2 > Q1 in thermochemical equation (is)A.2H2 (g) O2 (g) = 2H2O (g); H = Q1; 2H2 (g) O2 (g) = 2H2O (L); H = Q2B.S (g) O2 (g) = SO2 (g); H = Q1; S (s) O2 (g) = SO2

25、 (g); H = Q2C.C (s) 1/2O2 (g) = CO (g); H = Q1; C (s) O2 (g) = CO2 (g); H = Q2D.H2 (g) Cl2 (g) = 2HCl (g); H = Q1; 1/2H2 (g) 1/2Cl2 (g) = HCl (g); H = Q2.analysis A, due to water vapor into liquid water to heat, so the formation of liquid water than the heat to produce gaseous water, namely Q2 >

26、Q1; B, the solid sulfur into gaseous sulfur to absorb heat, so the gaseous sulfur combustion heat than solid sulfur burning out more heat, Q1 > Q2; C, CO generated heat, due to excessive oxygen will react with CO also emit heat, so Q2 > Q1, D Q1=2Q2.answer ACreaction the amount of heat release

27、d or absorbed by a reaction is closely related to the aggregation state of the reactant and the product.keyword the writing of reaction heat and thermochemical equation3 cases of hot furnace reaction: C (s) + O2 (g) = CO2 (g); H = - 392kJ/mol, to the furnace through vapour, the following reaction: C

28、 (s) + H2O (g) = CO (g) + H2 (g) Delta; H = CO + 131kJ/mol (g) + 1/2O2 (g) = CO2 (g); H = 282kJ/mol, H2 (g) 1/2O2 (g) = H2O (g); H = 241kJ/mol, from the above reaction to infer hot furnace in water vapor ()A. can't save fuel, but it can make the fire flash faster, B.It does not make the fire lig

29、hter, but it saves fuelC. not only burns the fire more quickly, but also saves fuel. D. does not make the fire any longer, nor does it save fuelanalysis the two aspects should be considered, one is able to make the fire instantly more prosperous, due to the furnace by water vapor, the following reac

30、tion: C (s) + H2O (g) = CO (g) + H2 (g), the formation of CO and H2 are combustible gas therefore, can make the fire more prosperous moment. The two is the ability to save fuel, according to law, C (s) H2O (g) = CO (g) + H2 (g); H = 131kJ/mol, CO (g) 1/2O2 (g) = CO2 (g); H = 282kJ/mol, H2 (g) 1/2O2

31、(g = H2O (G); H = 241kJ/mol, three equations are added together to obtain the total reactive C (s) + O2 (g) = CO2 (g); H = - 392kJ/mol, so with the same amount of carbon combustion heat, therefore can save raw materials.answer Aanalysis to master the use of laws of law for heat calculation.Keywords

32、writing and carbon group elements of reaction heat and thermochemical equation4 known vitriol when dissolved in water, the temperature of the solution decreases. 1mol made of anhydrous copper sulfate solution at room temperature, heat Q1kJ, and thermochemical equation is CuSO4 5H2O decomposition bro

33、chantite (s) = CuSO4 (s) 5H2O (L); H = Q2kJ/mol, then the relationship between Q1 and Q2 (is)A.Q1 > Q2 B.Q1 < C.Q1 = Q2 D. Q2 cannot be determinedanalysis CuSO4 5H2O from known (s) = Cu2+ (AQ) +SO42- (AQ) +5H2O (L); H = +Q (Q > 0). As.,CuSO4 (s) = Cu2+ (AQ) +SO42- (AQ); H = -Q1. 2.,1 - the

34、CuSO4 - 5H2O (s) = CuSO4 (s) + 5H2O (L); H = Q1+Q, according to Gass's Law: Q1+Q=Q2, so D is correct.answer Danalysis the solution of such questions often turns information into thermochemical equations, and then the correct conclusion can be drawn according to the laws of hess.Keywords writing

35、and oxygen group elements of reaction heat and thermochemical equationcase 5 known as amolC and bmolO2 (a > 2b), after sufficient reaction, the combustible material will be extracted again after combustion, and fully respond. Combustible material combustion, the heat released by p% by Mg, 0 degre

36、es of water absorption, make it boiling. If 1molC is known to burn as CO2, the heat released is qJ, try to figure out how much heat the 1molC will burn when it is fired into CO (c=4.2 * 103J/kg. C)analysis according to the problem that combustible material after combustion heat release for:. Know ag

37、ain:Therefore, the amounts of combustible substances in amolC and bmolO2 (a > 2b) are (a-2b) molC and 2bmolCO. If 1molCO is set to CO2 and the heat is xJ, the relation can be obtained:Xie jie:If the 1molC is set to CO and the heat is yJ, the following thermochemical equations are established:1.23

38、It is not difficult to find that "one type" = "Three - type" - type, that is, for the subject. It can be inferred:answer (aqp-4.2 * 104m) /2bpJThe subject is a comprehensive calculation of physics and chemistry. It is very difficult. Therefore, the key to solve the problem is to

39、analyze the problem of mining, important information hidden (i.e. a thermochemical equation additivity), two involved in the process of understanding the problem, namely the physical and chemical process, and calculated the amount of heat - bond linking these two processes (Q). Then the correct use

40、of the basic knowledge of physics and chemistry, the problem can be solved easily.Keywords writing and carbon group elements of reaction heat and thermochemical equationcase 6 the process of contacting sulphuric acid can be indicated as follows:Q: (1) what is the important role of heat exchangers in

41、 the production of sulphuric acid?(2) with T1, T2, T3, T4 respectively, said gas temperature import and heat exchanger, and T1 = 80 C, T3 = 600, T4 = 250 DEG C, the temperature of T2 SO2, O2 mixed gas into the chamber for contact (with inlet and outlet gas heat exchanger average specific heat are 0.

42、8kJ/ (kg? C).(3) assuming that the gas mixture entering the contact chamber is 20t per day, it is required that at least 80% tons of high-quality coal containing carbon per year can be saved per year compared to non heat exchangers The heating efficiency of known coal is 20%, C (s), +O2 (g), =CO2 (g

43、), and delta H=-393kJ/mol)analysis (1) by boiling furnace derived SO2 and O2, the temperature of the gas after the dust removing, had been greatly reduced after the removal of impurities, washing and so on, through the heat exchanger after the gas temperature is improved, which is conducive to the s

44、ubsequent reaction (i.e. SO2 synthesis of SO3). The oxidation reaction of SO2 is exothermic, and the temperature of SO3 and other gases derived from contact chamber is over 600 DEG C and can not be absorbed by concentrated sulfuric acid. After the heat exchanger, the temperature of SO3 drops, which

45、is beneficial to improve the absorption efficiency of concentrated sulfuric acid. In a word, the heat exchanger has the function of synergism and energy saving in the process of making H2SO4.(2) after the heat exchanger, the heat absorbed by SO2 and O2 = CM1 (T2-80 DEG C), and the amount of heat rel

46、eased by SO3 = cm2 (600 degrees -250 DEG C). According to the principle of physics and the law of conservation of mass, we know that Q (absorption) = Q (put), M1 = m2, so CM1 (T2-80 DEG C) = cm2 (600 degrees -250 DEG C), that is, T2 = 430 degrees celsius.(3) if the use of heat exchangers to 80 DEG S

47、O2, O2 preheated to 430 degrees, each year to provide heat for 20 * 103kg * 365 * 0.8kJ/ (kg? C) x (430 DEG -80 DEG =2.04 * 109kJ), effective heat per kilogram of high-quality coal supply is 5240kJ/kg, the use of quality the heat exchanger after high quality coal can be saved each year: 2.04 * 109kJ

48、/ (5240kJ/kg) =389.3t.answer (1) synergism energy saving (2) T2 = 430 DEG C (3) 389.3tanalysis the main use of formula Q=cm, t to examine the chemical reaction in the calculation of thermal effects.Keywords writing and oxygen group elements of reaction heat and thermochemical equation4. actual comba

49、t drills1. "shake ice" is a kind of instant cold drink. When in use, the chemical in the insulating layer of the beverage can is mixed with water, and then it is cooled by shaking. The chemical substance is ()A. sodium chloride, B. solid ammonium nitrate, C. solid sodium hydroxide, D. quic

50、klimeAnswer: B2. a dilute solution containing 20.0NaOH reacts with dilute hydrochloric acid to give off 28.7kJ of heat, indicating that the thermochemical equation for the neutralization of heat is correctA.1/2NaOH (AQ), +1/2HCl (AQ), =1/2NaCl (AQ), +1/2H2O (L), Delta H=+28.7kJ/molB.1/2NaOH (AQ), +1

51、/2HCl (AQ), =1/2NaCl (AQ), +1/2H2O (L), Delta H=-28.7kJ/molC.NaOH (AQ), +HCl (AQ), =NaCl (AQ), +H2O (L), Delta H=+57.4kJ/molD.NaOH (AQ), +HCl (AQ), =NaCl (AQ), +H2O (L), Delta H=-57.4kJ/molAnswer: D3. known: CH3COOH (AQ) +NaOH (AQ) = CH3COONa (AQ) +H2O H=Q1kJ / molH2SO4 (strong) +NaOH (AQ) = Na2SO4

52、(AQ) +H2O (1) H=Q2kJ / molHNO3 (AQ) +KOH (AQ) = KNO3 (AQ) +H2O (1) H=Q3kJ / molThe above reactions are all reactions in the solution, and the absolute value of Q1, Q2 and Q3 is the relation between themA.Q1 = Q2=Q3, B.Q2>Q1>Q3, C.Q2>Q3>Q1, D.Q2=Q3>Q1Answer: B4. thermochemical equation

53、: S (g) +O2 (g) =SO2 (g); H=-297.3kJ/mol, the correct analysis of the following statements is ()A.S (g) +O2 (g) =SO2 (L); | Delta H|>297.3kJ/mol B.1molSO2 bond energy is greater than the sum of 1molS and 1molO2 and the bond energyC.S (g) +O2 (g) =SO2 (L); | Delta H|<297.3kJ/mol D.1molSO2 1molS

54、 and 1molO2 is less than the sum of bond energy and bond energyAnswer: AB5. the white phosphorus air is heated to 260 DEG C can be transformed into red phosphorus. The following statement is correct ()A. WP into red phosphorus is an endothermic process than white phosphorus stable red phosphorus B.C

55、. WP into being red phosphorus induced reaction energy D. than stable red phosphorusAnswer: BC6. known: CH4 (g) 2O2 (g) = CO2 (g) 2H2O (L); H = 890kJ/molCO (g) 1/2O2 (g) = CO2 (g); H = 282.5kJ/mol. If the standard condition 89.6 is composed of CH4, CO, CO2 or mixed gas combustion can emit heat and g

56、enerate 1 million 10 thousand coke, 18 grams of liquid water, then mixed gas before combustion in CO accounted for the volume fraction is aboutA.40% B.50% C.60% D.70%Answer: B7. it is known that the combustion heat of the following alkanes is as follows:AlkanemethaneethanepropanebutanePentanehexaneC

57、ombustion heat / (kJ & mol-1)Eight hundred and ninety point threeOne thousand five hundred and fifty-nine point eightTwo thousand two hundred and nineteen point nineTwo thousand eight hundred and seventy-sevenThree thousand five hundred and thirty-six point twoFour thousand one hundred and sixty

58、-three point oneToday there is a 10L (in standard conditions) of a natural gas, assuming only two gases, methane and ethane, which emit heat when burning, 480KJ.Try to write (1) ethane gas combustion _ thermochemical equation;(2) the calculation of the volume fraction of _ methane in natural gas;(3) the approximate ru