Look at the four chemical reactions. Reaction 1: 2H2 + O2 → 2H2O Reaction 2: 2NaCl → 2Na + Cl2 Reaction 3: CaO + H2O → Ca(OH)2 R
1 answer:
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Answer:
(a) coal burning: chemical change
(b) ice melting: physical change
(c) mixing chocolate syrup with milk : physical change
(d) explosion of a firecracker: chemical change
(e) magnetizing of a screwdriver: physical change
Explanation:
A physical change changes the physical form or the appearance or the property of the substance, but the chemical composition of the matter remains the same. Such a change is reversible in nature.
Whereas; a chemical change involves a chemical reaction, resulting in the change in the chemical composition of the matter. A chemical change results in the formation of a new substance and is generally irreversible in nature.
(a) coal burning: It is a chemical change because the combustion of coal changes its chemical composition. When coal (carbon) is burned carbon dioxide is released. Irreversible in nature
(b) ice melting: It is a physical change because ice the solid phase of water melts to get converted to the liquid phase of water only and no change in the chemical composition is seen.
(c) mixing chocolate syrup with milk : It is a physical change because on dissolving chocolate syrup in milk, only the color of the milk changes, therefore there is change in the property. As, it involves mixing of two miscible liquids and does not involve any change in the chemical composition of either of the two liquids.
(d) explosion of a firecracker: it is a chemical process, as it involves combustion of an explosive material to produce carbon dioxide, carbon monoxide and water vapour. It is a chemical change because it involves change in the chemical composition. Irreversible in nature
(e) magnetizing of a screwdriver: It is physical change because on magnetization only the magnetic property of the screwdriver changes AND there is no change in the chemical composition of the matter.
Explanation:
Given that:
Distance traveled = 3150m
Average speed = 350m/min
Suggested speed = 375m/min
Unknown:
Time = ?
Solution:
Speed is the rate of change of distance with time.
it is mathematically expressed as;
speed =
Initial time using speed 350m/min can be calculated by making time the subject of the formula;
time taken =
time taken at speed of speed of 350m/min = = 9min
to seconds = 9 x 60 = 540 seconds
time taken at speed of 375m/min = = 8.4min
to seconds = 8.4 x 60 = 504 seconds.
It could have taken 504 seconds sooner saving 36 seconds.
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