Answer:
Explanation:
Valance electrons are loosely held electrons of an atom. They are involve in chemical reaction. Consider the example of metals such as group two metals. All these have two valance electrons. They needed six electrons to complete the octet or loses two valance electrons to get complete octet. Thus its easier to remove two electrons than getting six electrons. These metals remove two electrons and form cations.
Now consider the example of nonmetals such group sixteen. They needed two electrons to get complete octet or remove six electrons to get complete octet. Thus its easier for them to get two electrons and they form anion. When group two metals cation and group sixteen anions combine they form compound and chemical reaction occur.
Group two metals also combine with halogens. Two halogens atoms combine with one alkaline earth metal atom to cancel the charge and make compound neutral.
They react with oxygen and form oxide.
2Ba + O₂ → 2BaO
2Mg + O₂ → 2MgO
2Ca + O₂ → 2CaO
Oxygen carry -2 charge while Ca, Mg and Ba +2 and make the compound neutral because charges are equal in magnitude.
With sulfur,
Mg + S → MgS
Ca + S → CaS
Ba + S → BaS
Sulfer carry -2 charge while Ca, Mg and Ba +2 and make the compound neutral because charges are equal in magnitude.
You can not hear sound in vacuumed places like space. Wherever there is a high altitude, it makes it harder to hear sound and harder to breathe. Sound travels best in solids. Hope that helps a little bit.
Answer:
Explanation:
I₂ + 2 e = 2I⁻
I₂ converts itself into I⁻ by accepting electron . In this process it increases the oxidation number of element from which it takes electron . Hence it is an oxidizing agent .
Similarly O₂ is also an oxidizing agent .
O₂ + 4e = 2O⁻²
Al is a reducing agent .
Al = Al⁺³ + 3 e
Al gives 3 electrons to other element whose oxidation number is reduced . Hence it is reducing agent .
Similarly Cr is also a reducing agent .
Cr = Cr⁺³ + 3 e .
Answer : The enthalpy of combustion of 
will be -1775 kJ
Explanation :
According to Hess’s law of constant heat summation, the heat absorbed or evolved in a given chemical equation is the same whether the process occurs in one step or several steps.
According to this law, the chemical equation can be treated as ordinary algebraic expression and can be added or subtracted to yield the required equation. That means the enthalpy change of the overall reaction is the sum of the enthalpy changes of the intermediate reactions.
The combustion of will be,
The intermediate balanced chemical reaction will be,
(1) 
(2) 
(3) 
Now we are reversing the reaction 1, multiplying reaction 2 and 3 by 3 and then adding all the equations, we get :
(1) 
(2) 
(3) 
The expression for enthalpy of combustion of will be,
Therefore, the enthalpy of combustion of will be -1775 kJ
