Answer 20 on page 10 of the chemistry homework exercise for junior high school 20

The answer to the second question on page 10 of the Renjiao edition is: The main difference between physical change and chemical change is the formation of new substances. For example, when a candle melts, no new substance is produced, it is a physical change; Whereas the candle burns with the production of new substances is a chemical change.

The answer to the first question is :(1), (4), (6), (7), (8) is a physical change because there is no other new substance at the time of the change. 2), (3), and (5) are chemical changes because other new substances are formed when they change. Question 3 The answer is:

Physical Properties: 1258 Properties that do not require chemical changes to manifest.

Chemical Properties: 3467 Properties that manifest themselves in chemical changes.

Answer: (1), (4), (6), (7), (8) are physical changes because there is no other new substance at the time of the change. 2), (3), and (5) are chemical changes because other new substances are formed when they change. (2), (3) (5).

Physical Properties: 1258 Properties that do not require chemical changes to manifest.

Chemical Properties: 3467 Properties that manifest themselves in chemical changes.

1. The difference is: there is no material generation in physical change, and there is a mental substance generation in chemical change.

2. 14678 is a physical change, because no other matter is generated, and 235 is a chemical change, because when a change, a new substance is formed.

3. Because the combustion phenomenon is a chemical reaction, the change from solid to liquid is a physical change, and the propagation of light is also a physical change.

4. 1258 is a physical reaction because no matter is formed when it changes 3467 is a chemical reaction because there is a new substance that is formed or something else is generated!

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ab is the diameter of the circle o, c is a point on the circle o, ad, perpendicular to each other at point c, tangent, and pedal e proves that ac bisects dab

1.The fourth time to look at the first, second, third time, add 5g hydrochloric acid solid mass is less, indicating that 5g hydrochloric acid can just react with calcium carbonate, the fourth time but only less solids indicate that calcium carbonate has been reactive, the rest are impurities.

2 85% From the previous question, it can be seen that 2g of samples are impurities, and calcium carbonate is, which is obtained by dividing by one.

3 5t converted into grams is 5 * 10 6g, multiplied by the mass of calcium carbonate, and then divided by the molar mass of calcium carbonate 100g mol to obtain the amount of calcium carbonate substance, according to the equation caCO3 = cao + CO2 1mol calcium carbonate to generate 1mol carbon dioxide, the amount of calcium carbonate is the amount of carbon dioxide substance, and then multiplied by the molar mass of carbon dioxide 44g mol, converted into tons can be, the specific process is like this, generally written like this will not deduct process points.

1 Fourth.

2 The fourth gram of calcium carbonate complete reaction is impurity, so the mass of calcium carbonate in the 2g sample = 2g - =

caco3%= = 85%

The mass of CaCO3 in 5t limestone is 5t * 85% = then substituted into the equation to calculate.

High temperature. caco3 = cao+ co2

x proportional omitted solution x= answer omitted.

1) The fourth complete response.

2) The grams remaining after the fourth reaction are impurities (

3) Solution: Let the mass of carbon dioxide obtained be x

caco3=cao+co2

5t*85% x

Solve in column proportions and you're good to go.

Let the CO2 mass be x

mhcl=50g×38%=19g

caco3+2hcl==cacl2+h2o+co2↑73 44

19g x73/19g=44/x

x≈vco2=

Answer: The mass of the generated CO2 is, and the volume is.

Find the hydrochloric acid mass as 50* grams.

Equation 2HCl+CaCO3=CaCl2+CO2+H20 (relative molecular mass) 73 100 44

mass) 19 grams (corresponding to the calculation) is approximately equal to density multiplied by volume equal to mass. Ask for it yourself. In addition. Don't look for me if it's wrong... I'm not good at calculations. Hehe.

Carbon dioxide is produced The volume of carbon dioxide (standard condition) is.

1.Gases with no color and no smell in the air. Physics 2When water boils, it can turn into water vapor. Physics.

3.Food is digested in the human body and eventually turned into water, carbon dioxide, etc. Chemistry 4Sake can be made from grain. Chemistry.

5.The density of copper is, and the melting point is 1083Physics.

6.Carbon dioxide can muddy the edge of the clarified lime water. Chemistry 7Alcohol burns chemistry.

8.Alcohol is volatile physically.

(1), (2), and (5) are physical properties because these properties do not need to undergo chemical changes to manifest themselves.

3), (4), and (6) are chemical properties, because these properties must undergo chemical changes to manifest themselves.