Respuesta :
Answer:
1. The difference between a chemical change and a physical change is as follows;
In a physical change no new substance is formed while in a chemical change new substance are formed
Chemical change involves great amount of heat changes while physical change does not involves great amount of heat change except the latent heat changes which occur during changes of state
Physical change is easily reversed while a chemical change is not easily reversed
There is no change in the mass of a substance involve in physical change while in chemical change there is a change in the mass of a substance that undergoes such a change
2 . examples of physical and chemical changes
Physical change.
1. The magnetization and demagnetization of iron rods( the iron can be removed and no new substance will be formed)
11. The separation of mixtures by evaporation, distillation, fractional distillation, sublimation.( the separation techniques mentioned are physical change because they can be easily revised to get the original quantity back, like when water evaporates to vapour it can be retrieved back by cooling)
111. Changes in the states of matter such as melting of solids to liquids the freezing of liquids to solids, the vaporization of liquids to gases.( also changes of states are physical change because no new substance will be formed and it is easily reversible)
Chemical change
1. Fermentation and decay of substances .( new substance is formed which is the decayed substance)
11. The rusting of iron( rusting of iron is a chemical change because a new substance is formed. Which is the rusted iron)
111. The addition of water to quick lime I.e the slacking of lime. ( is a chemical change because a new substance is formed)
3. Boiling of water in a pot is a physical change because the water will evaporate into vapour at 100° Celsius and can be regained by cooling
Food digesting is a chemical change because a new substance will be formed , which is faeces.
Cooking an egg for breakfast is a chemical change because a new substance will be formed which is boiled egg and it can not be reversed.
Souring of milk is a chemical change because a new substance will be formed which is the soured taste
1a. A physical change:
I. It is easily reversible.
II. No new substances are formed.
III. There is no chage in mass of the substances undergoing such change.
IV. There is no great heat change except the latent heat change of state of dissolution, fusion and vaporization.
1b. A chemical change:
I. It is not easily reversible.
II. New substances are formed.
III. There is a change in mass of the substances undergoing such change.
IV. A considerable amount of heat change is usually involved.
2a. Three examples of physical changes:
I. Dissolution of table salt ( sodium chloride ) in water. This is a physical change because the constituents of salt solution ( salt + water ), being physically combined, can be separated by a physical separation technique called evaporation to dryness.
II. Melting of substances ( like ice ). An increase in temperature will melt ice to liquid water and a decrease in temperature of liquid water will convert it back to ice. Being a physical process the temperature does not change the chemical nature of the water.
III. Magnetization of iron rods. Iron rods can be magnetized and also demagnetized by hammering. The iron remains iron.
2b. Three examples of chemical changes:
I. Burning of substances ( like wood ). When wood is burnt it turns to ash. Since we cannot physical reverse the ash to get back the wood, it is a chemical change.
II. Decaying or decomposition of substances. When plants and animals decay they are converted to nitrogenous waste products, carbon dioxide and others, and they this expire in the process.
III. Dissolution of metals in acids. This is a chemical change. Many reactive metals above hydrogen in the activity series liberates hydrogen gas when dissolved in acids, producing other salts in the process. These products cannot be physically reversed to yield the starting materials ( reactants ) hence a chemical change.
3a. Boiling water in a pot is a physical change because we can reverse the process. When we cool the vapors resulting from the heated water we will get back the liquid water.
3b. Your food digesting is an overall chemical change. Though the food is initially broken down with the action of the teeth ( which is a physical change ), it is ultimately converted to nutrients and energy by the action of enzymes which is a chemical change.
3c. Cooking an egg for breakfast is a chemical change because there’s no physical process that is capable of turning the cooked egg into raw egg again.
3d. The milk souring in your fridge is a chemical change since it’s as a result of bacterial oxidation of lactose to lactic acid which is responsible for the sour taste. Lactose and lactic acid are both chemical compounds and the conversion of one chemical compound to another is a chemical change.
