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s2008m [1.1K]
2 years ago
10

What is the number of valence electrons in a calcium atom? * 8 2 18 20​

Chemistry
1 answer:
hoa [83]2 years ago
4 0

Answer:

2

Explanation:

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the molar enthalpy of formation of carbondioxide is -393kjmol. calculate the heat released by the burning of 0.327g of carbon to
Arte-miy333 [17]

This is equivalent to having a standard enthalpy change of reaction equal to  10.611 kJ

<u>Explanation</u>:

The standard enthalpy change of reaction,  Δ H ∘ , is given to you in kilojoules per mole, which means that it corresponds to the formation of one mole of carbon dioxide.

                                    C (s]  +  O 2(g] → CO 2(g]

Remember, a negative enthalpy change of reaction tells you that heat is being given off, i.e. the reaction is exothermic.

First to convert  grams of carbon into moles,

use carbon's molar mass(12.011 g).

                    Moles of C = mass in gram / molar mass

                                        = 0.327 g  / 12.011 g

                     Moles of C = 0.027 moles

Now, in order to determine how much heat is released by burning of 0.027 moles of carbon to form carbon-dioxide.

                                        =  0.027 moles C  \times 393 kJ

             Heat released  = 10.611  kJ.

So, when  0.027  moles of carbon react with enough oxygen gas, the reaction will give off  10.611 kJ  of heat.

This is equivalent to having a standard enthalpy change of reaction equal to  10.611 kJ

7 0
3 years ago
How many atoms are there in 15.0 grams of Sulfur (S)?
aev [14]

Answer:

C

Explanation:

Mol x Avogadro's number

Mol : mass / molar mass

Avogadro's no: 6.02E+23

6 0
3 years ago
When 1 mol of sodium nitrate, is dissolved in 1 cubic decimeter of water, 40 kJ of heat energy is absorbed. What is the drop in
vesna_86 [32]

Answer:

 1.0  ° C

Explanation:

The molar mass for Sodium Nitrate NaNO₃ = (23+14+(16×3)) = 85

Number of moles of NaNO₃  = mass of NaNO₃ /molar mass of NaNO₃

⇒ 17/85 = 1.38 moles

Since 1 mole of NaNO₃  dissolved in 1 cubic decimeter of water, 40 kJ of heat energy is absorbed.

when 1.38 mole of NaNO₃  dissolved in 1 cubic decimeter of water, x kJ of heat energy is absorbed..

Then; x kJ of 1.38 mole of NaNo₃ = 1.38 × 40 kJ  =55.2 kJ of heat absorbed.

Using the relation : Q = mcΔT  to determine the temperature drop ; we get:

55.2 = 17 × 4 (ΔT)

55.2  = 68 ΔT

ΔT= 0.8 ° C

ΔT ≅  1.0  ° C

Therefore, the drop in temperature when 17.0g of sodium nitrate is dissolved in 1 cubic decimeter of water is   1.0  ° C

7 0
3 years ago
What is the predominant intermolecular force in the liquid state of each of these compounds: hydrogen fluoride (HF), carbon tetr
telo118 [61]

Answer:

HF - hydrogen bonding

CBr4 - Dispersion

NF3 - Dipole-dipole

Explanation:

Hydrogen bonding occurs when hydrogen is covalently bonded to a highly electronegative atom such as fluorine, chlorine nitrogen, oxygen etc. Hence the dominant intermolecular force in HF is hydrogen bonding.

CBr4 is nonpolar because the molecule is tetrahedral and the individual C-Br dipole moments cancel out leaving the molecule with a zero dipole moment hence the dominant intermolecular force are the dispersion forces.

NF3 has a resultant dipole moment hence the molecules are held together by dipole-dipole interaction.

4 0
2 years ago
Sandy puts a paper clip on the table. Then, she puts a magnet near the paperclip. The paperclip begins to move.
Akimi4 [234]
Applied forces/or unbalanced:i hope that helps you
3 0
3 years ago
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