Answer:
7.71x10^23 molecules
Explanation:
Avogadro's # = 6.022x10^23
1.28 mol SiO2 x 6.022x10^23/ 1 mol SiO2 = 7.71x10^23 molecules
Answer : This reaction is an exothermic reaction.
Explanation :
Endothermic reaction : It is defined as the chemical reaction in which the energy is absorbed from the surrounding.
In the endothermic reaction, the energy of reactant are less than the energy of product.
Exothermic reaction : It is defined as the chemical reaction in which the energy is released into the surrounding.
In the exothermic reaction, the energy of reactant are more than the energy of product.
Enthalpy of reaction : It is the difference between the energy of product and the reactant. It is represented as
.
The balanced chemical reaction will be:

From the reaction we conclude that the heat energy is released during the reaction that means this reaction is an exothermic reaction.
Hence, the reaction is an exothermic reaction.
From
the problem statement, this is a conversion problem. We are asked to convert
from units of kilojoules to units of calories. To do this, we need a
conversion factor which would relate the different units involved. We either
multiply or divide this certain value to the original measurement depending on
what is asked. From literature, we will find that 1 kilojoule is equal to 239 calories. We do as follows:
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2.2125 kJ ( 239 calories / 1 kJ ) = 528.79 calories
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If this is a single atom of Boron, there should be 5 electrons as well. Boron as an electron configuration of 2-3 or 1s2 2s2 2p