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4 years ago

You break a pencil lead. Which statement is true?

Chemistry

1 answer:

aalyn [17]4 years ago

7 0

Answer:

<em><u>A physical change has occurred, with no energy change.</u></em>

Explanation:

When a pencil lead is broken there is not change of any chemical properties, therefore it is not a chemical change, but just a physical change. In this case the change is just the number of pieces and dimensions.

Chemical changes always involve the formation of new different substances; the bonds between the atoms of the starting substances (reactants) breake and new bonds are formed leading to new substances (products) with different chemical composition (arrange of atoms). Chemical changes occur through chemical reactions.

Hence, if there is not change on the chemical composition, you think on physical changes. Physical changes include change in shape, size, state of matter (e.g. solid, liquid, gas). In the case of a pencil lead breaking, it is a change in shape and size.

Also, since energy has not been absorbed or released during the change, the energy of the pencil lead before having been broken is equal to the sum of the energies of the pieces of pencil lead obtained. So, this is a physical change with no energy changes.

Some examples of physical changes that include change in energy are the change of state (e.g. solid to liquid or liquid to gas) and the dissolution of a compound.

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0.265g of an organic compound produced an evaporation 102cm³ of vapour at 373k and 775mmHg percentage composition of the constit

kumpel [21]

A. The molecular mass of the compound is 77.9 g/mol

B. The molecular formula of the compound is C₆H₆

<h3><u>Determination of the mole of the compound</u></h3>

We'll begin by calculating the number of mole of compound using the ideal gas equation as shown below:

Volume (V) = 102 cm³ = 102 / 1000 = 0.102 L

Temperature (T) = 373 K

Pressure (P) = 775 mmHg = 775 / 760 = 1.02 atm

Gas constant (R) = 0.0821 atm.L/Kmol

Number of mole (n) =?

n = PV / RT

n = (1.02 × 0.102) / (0.0821 × 373)

n = 0.0034 mole

<h3><u>A.</u><u> Determination of the </u><u>molecular mass</u><u> of the </u><u>compound</u><u>. </u></h3>

Mass = 0.265 g

Number of mole = 0.0034 mole

Molecular mass =?

Molecular mass = mass / mole

Molecular mass = 0.265 / 0.0034

Molecular mass of compound = 77.9 g/mol

<h3><u>B</u><u>. Determination of the </u><u>molecular formula</u><u> of the compound. </u></h3>

We'll begin by calculating the empirical formula of the compound.

Carbon (C) = 92.24%

Hydrogen (H) = 7.76%

Empirical formula =?

Divide by their molar mass

C = 92.24 / 12 = 7.69

H = 7.76 / 1 = 7.76

Divide by the smallest

C = 7.69 / 7.69 = 1

H = 7.76 / 7.69 = 1

Thus the empirical formula of the compound is CH

Finally, we shall determine the molecular formula.

Molecular mass = 77.9 g/mol

Empirical formula = CH

Molecular formula =?

Molecular formula = empirical × n = molecular mass

[CH]n = 77.9

[12 + 1]n = 77.9

13n = 77.9

Divide both side by 13

n = 77.9 / 13

n = 6

Molecular formula = [CH]n

Molecular formula = [CH]₆

Molecular formula = C₆H₆

Complete Question:

0.265g of an organic compound produced on evaporation 102cm cube of vapour at 373K and 775mmHg. Percentage composition of the constituent elements are 92.24% C and 7.76% H. Find the molecular mass and molecular formula of the composition.

Learn more about ideal gas equation:

brainly.com/question/14364992

Learn more about molecular formular:

brainly.com/question/512891

5 0

2 years ago

How do you know whether to use a lone pair or a double bond when drawing a Lewis dot structure?

Charra [1.4K]

Well that depends on the central atom. Remember each bond indicates another electron that is being shared with the central atom.
So CO4, carbon would be your central atom, with the 4 oxygen around it. There would be no double bonds because carbon only requires the 4 electrons provided by the oxygens, because of its location on the periodic table.
Nitrogen on the other hand is different. It's found in group 5 (5V) and has 5 valence electrons on its outer shell. So NO4 would have a central Nitrogen atom, with 3 oxygens providing a single bond, and one oxygen providing a double bond, because Nitrogen needs 5 electrons!
We learned it like this, the atom brought x amount of electrons to the party, x representing the valence electrons, and must leave with x electrons. It's silly but it works!
I hope I was able to help and clarify a few things up!

6 0

3 years ago

40 cm3 of acid were mixed with 60 cm3 of alkali in an insulated container. What name is given to this type of reaction?

Stells [14]

Answer:

neutralization reaction

6 0

2 years ago

The equilibrium system N2O4(g) 2NO2(g) was established in a 1.00-liter vessel. Upon analysis, the following information was foun

julsineya [31]

For the reaction, the equilibrium constant equation will be:

Kc = [NO₂]² / [N₂O₄]
Kc = (0.5)² / 0.025
Kc = 10

The answer is C.

3 0

3 years ago

Read 2 more answers

Which is a characteristic of aromatic hydrocarbons?

Jlenok [28]

Answer:

A. Alternating single and double bonds

Explanation:

Hydrocarbons i.e. hydrogen and carbon containing compounds, are grouped into two namely: aliphatic and aromatic hydrocarbons. Aliphatic hydrocarbons contains straight or branched chains of carbon and hydrogen atoms in their structure e.g. alkanes, alkenes etc.

On the other hand, aromatic hydrocarbons are cyclic hydrocarbons containing one or more cyclic rings. The benzene ring is the basis of all aromatic hydrocarbons and one characteristics of benzene is that it possesses an alternating single (-) and double bonds (=) in their structure.

Since benzene is a building constituent of aromatic hydrocarbons, an "alternating single and double bond" is a characteristics of aromatic hydrocarbons.

7 0

3 years ago