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Anonymous users2024-02-111.There is no new substance generated.
For example, the transformation of water into water vapor is a physical reaction, because no new substance is formed, and water vapor is still water.
For example, coal combustion produces carbon dioxide, and new substances are formed, so it is a chemical reaction.
2.Because candle burning produces water and carbon dioxide, it is a chemical change.
And because when you light a candle, the candle melts, so it's a physical change.
3.White solid powder, salty, soluble in water.
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Anonymous users2024-02-101. The formation of a new substance is a chemical change, e.g. 2
2 The candle burns, becomes hot and changes physically.
The candle burns, there is a smoke chemical change.
3. White solid, salty pH value is neutral.
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Anonymous users2024-02-091.Whether the substance has changed. For example, ice turns into water (physical change) and water splits into H2, O2 (chemical change).
2.The candle melts from a solid state to a liquid state (physical change), and the candle burns with substances such as CO2 and H2O (chemical change), so there are both physical and chemical changes when lighting a candle.
3.Described in terms of color, hardness, etc.
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Anonymous users2024-02-081 Physical change: no new substances are formed during the change process Example: gasoline volatilization.
Chemical change: In the process of change, new substances are formed e.g., magnesium belt combustion The product is white powder.
2 When a candle is lit, the process of the candle melting is a physical change, whereas the process of the candle burning is a chemical change.
3 Salt: NaCl is neutral white particles (there is a sentence on the quality inspection that says this, you can judge whether I am right: physical properties are properties that can be manifested by substances without chemical changes, generally some properties that are manifested when the composition of the substance does not change and the aggregation state of the substance changes, or properties that can be directly perceived and measured).
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Anonymous users2024-02-071.Whether new substances are formed. Physical Change: Wet clothes are dried. Chemical changes: food spoilage.
2.When the candle burns, the candle keeps getting shorter, which is a physical change. When a candle is burned, it produces a new substance such as CO2, which is a chemical change. Therefore, candle burning is both a physical and a chemical change.
3.Table salt is a colorless and transparent crystal that is easily soluble in water.
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Anonymous users2024-02-06Whether new substances are formed. Water vaporization is a physical change, and the decomposition of water to produce hydrogen and oxygen is a chemical change.
Because candle melting is a physical change, candle burning is a chemical change (producing carbon dioxide and water).
Colorless, odorless, transparent crystals.
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Anonymous users2024-02-05It is an acidic oxide, so strong bases can be, generally use NaOH, the chemical equation is 2NaOH + 2CO2 = Na2CO3 + H2O, Ca(OH)2 does not work because Ca(OH)2 is slightly soluble in water.
2.The greater the purity of the oxygen, the more fully it reacts with the carbon in the pig iron, and the greater the purity of the steel being refined.
3.Add the mass of the reactants, and then subtract the mass of the remainder to obtain the mass of the generated gas, A is, B is, C is the data of the classmate is wrong, it should be, it is still calculated in this way, but B participates in the reaction of the two reactants are the least, so the sample of B is completely reacted; The mass fraction equation is 2Fe + H2SO4 = FeSo4 + H2, and the mass of hydrogen is substituted (, to find the mass of Fe, and then divide by 9g of the sample mass to calculate the mass fraction of iron in the sample; Knowing the mass of Fe, you can find the mass of FeSO4 (solute), and the mass of the solvent is the mass of the reactant minus the mass of hydrogen.
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Anonymous users2024-02-04Ca(OH)2 solution.
The concentration of Ca(OH)2+CO2=CaCO3+H2O is large, and the reaction is more thorough.
Comrade, there is a problem with the data.
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Anonymous users2024-02-03By clarifying lime water, the oxygen content of Ca(OH)2+CO2=CaCO3+H2O pure oxygen is much higher than that of air, so that the contact area between the metal and oxygen is large and the reaction is sufficient, thereby increasing the efficiency.
The third question is too troublesome to calculate, so you can use a calculator to calculate it yourself.
Add the mass of the reactants, and then subtract the mass of the remainder to obtain the mass of the generated gas, A is, B is, C is the data of the classmate is wrong, it should be, it is still calculated in this way, but B participates in the reaction of the two reactants are the least, so the sample of B is completely reacted; The mass fraction equation is 2Fe + H2SO4 = FeSo4 + H2, and the mass of hydrogen is substituted (, to find the mass of Fe, and then divide by 9g of the sample mass to calculate the mass fraction of iron in the sample; Knowing the mass of Fe, you can find the mass of FeSO4 (solute), and the mass of the solvent is the mass of the reactant minus the mass of hydrogen.
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Anonymous users2024-02-02The force area of the cylinder is r 2, r=45mm=. The work done by the gas is equal to the pressure (pressure multiplied by area) multiplied by the distance of the force (100mm=: type dispersed.
The Type 490 diesel is a four-stroke engine (intake, compression, work, exhaust), so it takes two revolutions to complete a power stroke. The power is 4*. If I'm mistaken, it's a two-stroke, and it's doubled.
I'm using the calculator directly, not omitting it.
"light" i.e. (volatile), "irritable" i.e. (flammable and explosive).
1.Let a meal of gasoline provide a calorie of q, and the amount of methanol gasoline sought is x tons. So (here, the heat produced by the complete combustion of each kilogram of methanol is only half of that of gasoline oil, so the heat provided by methanol in methanol gasoline is. Solution x = tons.
2.Tons of gasoline can be saved.
Yuan. 20-16,4g is the mass of the oxygen element taken away by hydrogen, that is, 4 16 = o, that is, cuo, the mass is 20g, and the mass fraction is 100%.
2kmno4==
k2mno4+mno2+o2, so, the reduced mass is oxygen, yes, so the original potassium permanganate in the sample is, is, the purity is.
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Anonymous users2024-02-01(1)16
2) (3) grams.
Calculation process: m(co)=50+
M total (HCL) = 15g
m(na₂co₃)=
The mass of HCl reacting with Na Co is:
The mass of HCl reacting with NaOH is:
m(naoh)=
The mass of sodium hydroxide in the sample is:
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It's still too late, but it depends on your child's level. How bad is "bad"? If you don't know it by a large margin, it's a bit difficult to tutor at this time, if it's just a partial incomprehension, find a teacher to give him a penetration, and do more questions to make up for it. >>>More
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First of all, we must put down some difficult and deceitful questions, focus on reviewing the basic content in the textbook according to the exam syllabus, don't do a lot of questions, pay attention to the basics, there are more chemical memorizations, and physics should summarize more, get the test questions thoroughly, and communicate more with the teacher, anyway, if you are going to graduate, you don't have to be afraid of him, so if you don't understand, you have to ask, it is a normal thing to be nervous before the exam, don't worry too much. Confidence is the most important thing. Come on, dear, I wish you a good result
First of all, your attitude is worth affirming, on the one hand, you have to learn the ins and outs of knowledge, learn how it came about, how it should be used, and the interconnection between the knowledge points, so as to achieve the real will, on the other hand, pay attention to the summary, science things, thinking and methods are more important than the knowledge points themselves, the purpose of doing questions is to improve thinking, refine methods, not to do questions for the sake of doing questions, and moreover, there is a good way, that is, to tell others the topics you have done, you can tell your classmates, You can also tell parents, if you can explain a problem, it means that you really understand. These things are more active methods, if you can't do them, then you can only use passive methods, that is, repeated review and repetition.