Science · X-Factor Notes
Physical and Chemical Changes, Solution revision notes for UPPCS Prelims.
High-Yield Revision| Concept | What to remember | Asked in UPPCS |
|---|---|---|
| Physical Change | Changes the physical traits (shape, size, color) of a substance without altering its internal chemical structure. It is generally a reversible process. | |
| Example of Physical Change | Change of water into vapour is a physical change. Dissolving sugar in water is a physical change, as sugar can be recovered by evaporating the water. | UPPCS (Pre) 1992 |
| Chemical Change | A process where atoms are rearranged to form a new substance with a different chemical composition. It is an irreversible process. | |
| Example of Chemical Change |
| Concept | What to remember | Asked in UPPCS |
|---|---|---|
| Effect of Impurities on Boiling Point | When some impurities are mixed with a liquid, its boiling point increases. | |
| Freezing Point Depression | Temperature below |
| Concept | What to remember | Asked in UPPCS |
|---|---|---|
| Purification of Solids | Distillation is generally used for purifying liquid impurities. It is not useful for the purification of solid impurities; methods like sublimation and crystallization are used for solids. | U.P. R.O./A.R.O. (Pre) (Re. Exam) 2016 |
| Souring of milk is an example of a chemical change. Softening of vegetables when cooked alters the molecular composition and is irreversible, thus it is a chemical change. |
| Chemical Reaction Rate | A chemical reaction becomes faster at a higher temperature because molecular motion becomes more rapid. | UPPCS (Pre) 2017 |
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| Pasteurization | A process where milk is first heated up for a longer time and then cooled. This process is related to changes in properties like enzyme activity. | U.P. Lower Sub. (Pre) 1998 |
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| Exothermic Processes | Processes that release energy (heat). Examples include the dilution of an acid () and the reaction of water with quick lime. |
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| U.P. Lower Sub. (Pre) 1998 |
| Unsaturated Solution Volume | If an unsaturated sugar solution is prepared by mixing grams of sugar with half litre of water, the volume of the solution remains constant (or does not change). | UPPCS (Pre) 2017 |
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| Osmosis | The process where the solvent moves through a semi-permeable membrane from a region of lower solute concentration to a region of higher solute concentration to equalize concentration. |
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| Reverse Osmosis | External pressure is applied upon the concentrated solution to reverse the movement of the solvent (from concentrated to dilute solution). This technique is used to purify solutions. |
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