Chemistry Grade 10

Gujranwala Board 10th Class Past Papers Chemistry

 

Section A-(MCQs)

i)  The nitrogen present in urea is used by plants to synthesize ______                                                                                                                                                            (Mark 1)

A. sugar
B. proteins
C. fats
D. DNA
Answer:
B. proteins

Section B-(Short Questions)

Q.2 i) Write expression for the equilibrium constant for the reaction.                                                                                                                                                      (Marks 2)
                                    N2 + 3H2 ⇌  2NH3

Answer:
For the reaction,
Rate of forward reaction:    Rf = kf [N2] [H2]3
Rate of reverse reaction:    Rr = kr [NH3]2
Equilibrium constant:
Kc = [NH3]2 / [N2] [H2]3

Section C-(Long Questions)

Q.9 b) What is ozone? How concentration, of ozone remains constant in stratosphere?                                                                                                              (Marks 3)

Answer:
Ozone
Ozone is an allotropic form of oxygen consisting of three oxygen atoms. The ozone layer is a belt of naturally occurring ozone gas above Earth and serves as a shield from the harmful ultraviolet radiation emitted by the sun. The ozone layer lies between 10 and 50 km above the Earth's surface. It is in a region of the atmosphere called the Stratosphere.
It is constantly being formed and broken down in the high atmosphere above Earth, in the stratosphere. On absorbing UV radiation, ozone molecule breaks up to form an oxygen molecule and atomic oxygen.
O3 → O2 + O
Atomic oxygen reacts readily with an oxygen molecule to form ozone, thus releasing heat.
O2 + O → O3 + heat
If there is no external intervention, the rate of ozone destruction and formation remains equal.

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