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Which of the following is a reversible change?
Melting of ice is a physical change in which substance changes its physical state but not properties. Hence it is a reversible change in which melted ice can freeze again by decrease in temperature.
In a chemical change:
In a chemical change, the molecules in the reactants interact to form new substances. In a physical change, like a state change or dissolving, no new substance is formed. Explain that another way to say that no atoms are created or destroyed in a chemical reaction is to say, “Mass is conserved.”
Which of the following is an example of physical change?
Boiling waterBoiling water is an example of a physical change and not a chemical change because the water vapor still has the same molecular structure as liquid water (H2O). If the bubbles were caused by the decomposition of a molecule into a gas (such as H2O →H2 and O2), then boiling would be a chemical change.
In a chemical change:
All chemical reactions involve energy. Energy is used to break bonds in reactants, and energy is released when new bonds form in products. Endothermic reactions absorb energy, and exothermic reactions release energy.
While making a wooden wheel, the iron rim is made slightly smaller than wooden wheel. Why?
Choose the correct option.
Electric wires or telephone wires become tight during winter but sag a little during summer, because they are made of metal which:
Because the cores of overhead wires are made from copper. Metals expand with heat and contract with cold. In winter, the reverse happens - the lines contract and tighten up.
Which of the following is not an example of the changes that occur by mixing two substances?
The changes which are not useful to us and may cause harm are called undesirable changes. Which of the following is/are example(s) of undesirable changes?
Read the activity carefully.
1. Take two flasks, flask A and flask B.
2. In both of the flasks, take some lemon juice.
3. In flask A, add washing soda in the lemon juice.
4. In flask B, add salt in the lemon juice.
Q. Which could be the observation of this experiment?
Physical changes can be generally reversed. Which of the following is an example of a physical change?
1. Zinc oxide, on heating, changes to yellow colour. However, on cooling, its colour changes to white.
2. When a piece of iron is stroked with a permanent magnet, it gets magnetized. However, if the magnetized iron is hammered, it loses its magnetism.
3. Wax, on being heated, changes into its liquid state. However, liquid wax changes into solid on cooling.
Look at the following graph. It represents the energy consumption of a reaction. What kind of a change is it?
Shahna took a small amount of lead nitrate in a dry test tube, holding the test tube with a test-tube holder. She put the test tube over the flame of the burner, and heated it. Soon a brown gas with a pungent smell is produced. The gas turns blue litmus red. She also observes a yellow solid residue remains in the test tube.
Q. Conclusion of the above experiment may be:
In which of the following statements is it proven that energy keeps on moving from one source to another and that it is not static?
What property remains the same during physical or chemical changes?
During a physical change, the arrangement of particles may change but the mass, number of atoms and number of molecules will stay the same. During a chemical change, the mass and number of atoms is conserved, but the number of molecules is not always the same. Chemical reactions involve large changes in energy.
Which of the following does not indicate a chemical change?
However, one thing that does not indicate a chemical change is the change of shape. When the new form occurs from these two substances are mixed mean that it could be something else like a physical change. There are different types of chemical changes. One is the chemical change, and the other is organic change.
What is common among the following phenomena?
1. A slice of apple, if kept in the open, develops a brown colour.
2. Burning of magnesium ribbon.
3. A new substance is formed during this change.
Look at the flowchart and study it carefully.
Q. Which of the following is correct?
A teacher kept a beaker of water on a hot plate. The beaker is shown before and after the hot plate is turned on.
Q. What evidence points to the fact that water is changing state?