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3 years ago

What is the density of a block of marble that occupies 311 cm cubed and has a mass of 853 g?

Chemistry

1 answer:

kompoz [17]3 years ago

6 0

Mass/volume=density
853/311=?
density is about 2.74

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You break a pencil lead. Which statement is true?

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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.

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7 0

3 years ago

2. Nitrogen has two naturally occurring

kvv77 [185]

Answer:

Suppose that:

Mass of N-14= 14

and Mass of N-15= 15

fraction N-14 x 14 + fraction N-15 x 15 = 14.007

now.. if the fractions were =, that is if fraction N-14 = fraction N-15 = 0.5, then...

0.5 x 14 + 0.5 x 15 = 14.5

more N-15 would make that number larger...

0.3 x 14 + 0.7 x 15 = 14.7

let x = abundance of N-14, then (1-x) = abundance of N-15, and we could solve for x.

(X)x14 + (1-X)x 15 = 14.007

14X + 15 - 15X = 14.007

X = 0.993

the relative abundance of N-14 = 99.3%

the relative abundance of N-15 = 0.7%

So, according to the above explanation N-14 is abundant

Explanation:

Suppose that:

Mass of N-14= 14

and Mass of N-15= 15

fraction N-14 x 14 + fraction N-15 x 15 = 14.007

now.. if the fractions were =, that is if fraction N-14 = fraction N-15 = 0.5, then...

0.5 x 14 + 0.5 x 15 = 14.5

more N-15 would make that number larger...

0.3 x 14 + 0.7 x 15 = 14.7

let x = abundance of N-14, then (1-x) = abundance of N-15, and we could solve for x.

(X)x14 + (1-X)x 15 = 14.007

14X + 15 - 15X = 14.007

X = 0.993

the relative abundance of N-14 = 99.3%

the relative abundance of N-15 = 0.7%

So, according to the above explanation N-14 is abundant

8 0

2 years ago