Is a cold and b is warm? Please help

Answer:

Sodium Carbonate

Explanation:

Sodium carbonate is made of three elements, that are, sodium, carbon and oxygen.

Its formula is Na2CO3.

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Answer:

Melting is endothermic, so the air temperature decreases.

Explanation:

Hello there!

In this case, according to the given statement, it is possible to infer that the ice is melt because energy is applied to the ice and thereafter its temperature increases; this is possible because the joined particles of a solid substance need energy to undergo such a separation that they become more far away to each other and therefore transcend to the liquid phase due to the new molecules arrangement. Thus, the answer is Melting is endothermic, so the air temperature decreases because as the ice heats up, the air cools down as it gives it energy to the ice.

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Answer:

There are 12 nanoseconds in [tex]1.2\times 10^{-8}\ s[/tex].

Explanation:

We need to convert [tex]1.2\times 10^{-8}\ s[/tex] to nanoseconds.

We know that,

[tex]1\ s=10^9\ ns[/tex]

Now using unitary method to solve it such that,

[tex]1.2\times 10^{-8}\ s=1.2\times 10^{-8}\ \times 10^9\\\\=1.2\times 10\\\\=12\ ns[/tex]

So, there are 12 nanoseconds in [tex]1.2\times 10^{-8}\ s[/tex].

Answer: 480 kJ of energy is released when 3.5 mol of [tex]C_2H_4[/tex] reacts.

Explanation:

The balanced chemical reaction is:

[tex]C_2H_4(g)+H_2(g)\rightarrow C_2H_6(g)[/tex]  [tex]\Delta H=-137kJ[/tex]

Thus it is given that the reaction is exothermic (heat energy is released) as enthalpy change for the reaction is negative.

1 mole of [tex]C_2H_4[/tex] on reacting gives = 137 kJ of energy

Thus 3.5 moles  of [tex]C_2H_4[/tex] on reacting gives = [tex]\frac{137}{1}\times 3.5=480 kJ[/tex] of energy

Thus 480 kJ of energy is released when 3.5 mol of [tex]C_2H_4[/tex] reacts.