Download App

Hydrogen — Chemistry STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 ScienceChemistryHydrogen5 Marks
Question
Give reasons:
Lakes freeze from top towards bottom.
✓

Answer

During severe winter, the temperature of water in the lake keeps on decreasing. Since cold water is heavier, it keeps on going into the interior of the lake while warm water keeps on coming to the surface of the lake. This process continues till the temperature of entire water of lakes becomes 4°C. Since density of water is maximum at 277K, any further decrease in the temperature will decrease its density. As a result, the temperature of the surface water keeps on decreasing and it ultimately freezes. Now, any further decrease in the temperature will decrease the temperature of water below 4°C. This process continues and as a result, the lakes keep on freezing from top to bottom.

Need a full question paper?

Generate a complete, print-ready paper with questions like this in minutes — across 16+ boards, with answer keys.

Start Generating Free

Explore more

More "5 Marks Questions" from Hydrogen→Hydrogen — all question types→Chemistry STD 11 Science question papers→Gujarat Board STD 11 Science question papers→Gujarat Board question paper generator→

Similar questions

Which of the following reactions involve homogeneous equilibria and which involve heterogeneous equilibria?
  1. $2\text{N}_2\text{O(g)}\rightleftharpoons2\text{N}_2(\text{g})+\text{O}_2\text{(g)}$
  2. $2\text{NH}_3\text{(g)}\rightleftharpoons\text{N}_2(\text{g})+3\text{H}_2\text{(g)}$
  3. $2\text{Cu}(\text{NO}_3)_2(\text{s})\rightleftharpoons2\text{CuO(s)}+4\text{NO}_2(\text{g})+\text{O}_2(\text{g})$
  4. $\text{CH}_3\text{COOC}_2\text{H}_5(\text{aq})+\text{H}_2\text{O}\text{l}\\\rightleftharpoons\text{CH}_3\text{COOH(aq)}+\text{C}_2\text{H}_5\text{OH(aq)}$
  5. $\text{Fe}^{3+}(\text{aq})+\text{3OH}^-\text{(aq)}\rightleftharpoons\text{Fe(OH)}_3(\text{s})$
→
The first ionization enthalpy values (in $\mathrm{kJ} \mathrm{~mol}^{-1}$ ) of group 13 elements are:
B Al Ga In Tl
801 577 579 558 589
How would you explain this deviation from the general trend?
→
What do you understand by the term “non-stoichiometric hydrides”? Do you expect this type of the hydrides to be formed by alkali metals? Justify your answer.
→
Explain the reason for the fusion of an organic compound with metallic sodium for testing nitrogen, sulphur and halogens.
→
  1. The energy associated with Bohr's first orbit is $-2.18 \times 10^{-18}J atom^{-1}$. What is the energy associated with fifth orbit?
  2. The work function for Caesium atom is $1.9 eV$.
Calculate the threshold wavelength.
[Given: $1 eV = 1.6 × 10-19J$]
  1. How many subshells are associated with $n = 4$?
→
Explain isomerism and nomenclature of alkynes.
→
Balance the following redox reactions by ion-electron method:
$MnO_4^-(aq) + I^-(aq) \rightarrow MnO_2(s) + I_2(s)$ (in basic medium).
→
What is electron gain enthalpy? State the periodic trend of it in groups and periods.
→
What are the reactions involved for ozone layer depletion in the stratosphere?
→
What is the type of hybridisation of carbon atoms marked with star.
  1. $\text{CH}_{3}=\text{CH}-\text{C}-\text{O}-\text{H}$
  2. $\text{CH}_{3}-\text{CH}_{2}-\text{OH}$
  3. $\text{CH}_{3}-\text{CH}_{2}-\text{C}-\text{H}$
  4. $\text{CH}_{3}-\text{CH}=\text{CH}-\text{CH}_{3}$
  5. $\text{CH}_{3}-\text{C}\equiv\text{CH}$
Comprehension given below is followed by some multiple choice questions. Each question has one correct option. Choose the correct option.
Molecular orbitals are formed by the overlap of atomic orbitals. Two atomic orbitals combine to form two molecular orbitals called bonding molecular orbital (BMO) and anti bonding molecular orbital (ABMO). Energy of anti bonding orbital is raised above the parent atomic orbitals that have combined and the energy of the bonding orbital is lowered than the parent atomic orbitals. Energies of various molecular orbitals for elements hydrogen to nitrogen increase in the order.
Different atomic orbitals of one atom combine with those atomic orbitals of the second atom which have comparable energies and proper orientation. Further, if the overlapping is head on, the molecular orbital is called ‘Sigma’, and if the overlap is lateral, the molecular orbital is called ‘pi’. The molecular orbitals are filled with electrons according to the same rules as followed for filling of atomic orbitals. However, the order for filling is not the same for all molecules or their ions. Bond order is one of the most important parameters to compare the strength of bonds.
→