Answer:
0.22 grams of magnesium
This seems too low, so check the calculations/
Explanation:
How is the heat delivered? Is the magnesium hot and added to the water? If so, at what temperature.
Is the heat generated from an exothermic chemical reaction?
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I'll assume here that the heat comes from the reaction of magnesium with water. The balanced equation is:
Mg + 2H2O = Mg(OH)2 + H2
It has a heat of reaction of −924.7 kJ/mol.
We need enough Mg to heat 30 ml of water from 22°C to 90°C. The specific heat of water is needed. It is 4.184 J/g-K. It tells us that 4.184 Joules are needed to raise the temperature of water by 1 degree K.
30 ml of water with density 1 gram/ml means we have 30 grams of water. (We'll ignore the water that is added from the chemical reaction.).
Lets calculate the Joules required to raise 30 grams of water from 22°C to 90°C. Note that the specific heat has units of g and Kelvin. Since we need a temperature change, the number value for ΔT is the same for both °C and °K. So the temperature change is +68°K.
We can now calculate the Joules required:
(30 grams H2O)*(4.184 J/g-K)*(+68°K) = 8535.4 Joules or 8.5 kJ to 2 sig figs.
The Mg/H2O heat of reaction of −924.7 kJ/mol. will allow us to calculate the amount of Mg needed to supply 8.5 kJ. The minus sign tells us that the reaction RELEASES energy (the energy leaves the "system" of Mg and H2O).
Calculate the moles of Mg needed to release 8.5 kJ:
(924.7 kJ/mole)*(x moles) = 8.5 kJ
x moles = 0.0092 moles
Whoa. That is only (0.0092 moles)*(24.03 g/mole) = 0.22 grams of magnesium
This seems low to me, so check on the heat of reaction figure I used. And don't let the hydrogen get away.
K and Br
C and Cl
Fe and Ni
Ionic bonds are formed between a metal and a nonmetal. Among the pairs given, K and Br satisfy these conditions and will form an ionic bond.
The question is asking about ionic bonds, which are formed when one atom donates an electron to another atom. This occurs between a metal and a nonmetal due to their differences in electronegativity.
Looking at the options, N and O are both nonmetals, C and Cl are also both nonmetals, and Fe and Ni are both metals, so they would not form ionic bonds. On the other hand, K (a metal) and Br (a nonmetal) have a difference in electronegativity such that K can donate an electron to Br, forming an ionic bond. Therefore, the pair that would form an ionic bond is K and Br.
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a. 8
b.16
c.32
d.64
32 Electrons
In statement the letter "n" specifies the Principle Quantum Number. Principle Quantum number is main energy level of an atom. Hence, n = 4 means we are talking about the fourth energy level or fourth shell of an atom.
Also, the number of electrons present in any main energy level are calculated by using following formula,
2n²
Hence, as,
n = 4
So, by putting this value in above formula,
2 (4)²
2 (16)
32
The maximum number of electrons that can be accommodated in the n=4 shell is 32.
(Option C).
The maximum number of electrons that can be accommodated in the n=4 shell can be determined using the following formula.
maximum electrons = 2n²
where;
The given parameters include;
n = 4
The maximum number of electrons that can be accommodated in the n=4 shell is calculated as;
maximum electrons = 2n²
maximum electrons = 2 (4²)
maximum electrons = 32
Learn more about maximum electron in shell here: brainly.com/question/4177923
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