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प्रश्न
Write any two observations in an activity which may suggest that a chemical reaction has taken place. Give an example in support of your answer.
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उत्तर
Two observations that may suggest that a chemical reaction has taken place are
(i) evolution of a gas and
(ii) change in temperature.
For example, zinc granules react with dilute sulphuric acid to evolve hydrogen gas, which is easily observed by the bubbles of hydrogen gas appearing around zinc granules. Also, the flask becomes hot, which shows heat is evolved during the reaction—that is, change in temperature.
Zn + H2SO4 → ZnSO4 + H2↑ + Heat
संबंधित प्रश्न
Methyl orange is used as an indicator. It shows colour change in acid, base and neutral substance. Tabulate your result as follows:
| Indicator | Colour change | Inference |
| Methyl Orange | No change | ...................... |
| .................... | Acid | |
| Yellow | ....................... |
When hydrogen is passed over copper oxide, copper and steam are formed. Write a balanced equation for this reaction and state which of the chemicals are elements.
Give one example of an exothermic reaction.
Is Electrolysis of water an endothermic reaction or an exothermic reaction?
Balance the following chemical equation:
Write the balanced equation for the following chemical reaction.
\[\ce{Barium chloride + Aluminium sulphate -> Barium sulphate + Aluminium chloride}\]
Balance the following equation. Also name the products formed.
`"Mg" + "O"_2 → "MgO"`
A student weighed some raisins and recorded the weight as ‘x’. She then soaked the raisins in distilled water. After about 2 hours she removed the raisins, wiped them dry and weighed them again, and recorded that as ‘y’. The percentage of water absorbed by raisins may be determined using the relationship.
Balance the following equation:
S + H2SO4 → SO2 + H2O
Choose the correct answer from the options given below.
The formula of sodium carbonate is Na2CO3 and that of calcium hydrogen carbonate is
Write the balanced chemical equation of the following reaction. sodium hydroxide + sulphuric acid → sodium sulphate + water
Write the balanced chemical equation of the following reaction. iron + sulphuric acid → ferrous sulphate + hydrogen.
Write the balanced chemical equation of the following reaction.
iron pyrites(FeS2) + oxygen → ferric oxide + sulphur dioxide
1 g of copper powder was taken in a China dish and heated. What change takes place on heating? When hydrogen gas is passed over this heated substance, a visible change is seen in it. Give the chemical equations of reactions, the name and the color of the products formed in each case.
Write the name and molecular formula of a carbon compound having its name suffixed with "-ol" and having two carbon atoms in its molecule. With the help of a chemical equation indicate what happens when this compound is heated with excess conc. H2SO4.
A chemical reaction is generally accompanied by certain external indications or characteristics. These include – change of – (a) colour (b) state (c) smell (d) evolution of gas (e) formation of precipitate (f) evolution or absorption of heat. With reference to change of colour – state the change in colour seen when the following are heated – zinc carbonate.
Write word equation for the following chemical reaction given below. Also state the observation seen in the case.
\[\ce{ZnCo3->[\triangle] ZnO + CO2}\]
The following reaction is an example of a `4"NH"_3("g") + "SO"_2 -> 4"NO"("g") + 6"H"_2"O"("g")`
- displacement reaction
- combination reaction
- redox reaction
- neutralisation reaction
A student took a small amount of copper oxide in a conical flask and added dilute hydrochloric acid to it with constant stirring. He observed a change in colour of the solution.
- Write the name of the compound formed and its colour.
- Write a balanced chemical equation for the reaction involved.
