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3 years ago

You break a pencil lead. Which statement is true?

Chemistry

1 answer:

aalyn [17]3 years ago

7 0

Answer:

A physical change has occurred, with no energy change.

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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Explain why a single atom of hydrogen cannot produce all four hydrogen spectral lines simultaneously.

brilliants [131]

When the electron in a hydrogen atom transitions from a high energy state to a lower energy state, the energy lost from the electron is used to produce a photon corresponding to the loss of energy. That photon will correspond to exactly 1 wavelength. And since a hydrogen atom has only 1 electron, at any given moment, it can only produce 1 photon. And in order to simultaneously produce 4 photons for 4 spectral lines, that would require a simultaneous transition of 4 electrons which is 3 too many for a hydrogen atom.

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3 years ago

Question 2 Calculate the pH of a solution that has an acetic acid concentration of 0.05 M and a sodium acetate concentration of

Eva8 [605]

Answer : The pH of the solution is, 4.9

Explanation : Given,

Dissociation constant for acetic acid = $K_a=1.8\times 10^{-5}$

Concentration of acetic acid = 0.05 M

Concentration of sodium acetate = 0.075 M

First we have to calculate the value of $pK_a$ .

The expression used for the calculation of $pK_a$ is,

$pK_a=-\log (K_a)$

Now put the value of $K_a$ in this expression, we get:

$pK_a=-\log (1.8\times 10^{-5})$

$pK_a=5-\log (1.8)$

$pK_a=4.7$

Now we have to calculate the pH of buffer.

Using Henderson Hesselbach equation :

$pH=pK_a+\log \frac{[Salt]}{[Acid]}$

$pH=pK_a+\log \frac{[CH_3COONa]}{[CH_3COOH]}$

Now put all the given values in this expression, we get:

$pH=4.7+\log (\frac{0.075}{0.05})$

$pH=4.9$

Therefore, the pH of the solution is 4.9.

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2 years ago

Carbohydrates like sugars and starches are made of only three elements: carbon (C), hydrogen (H), and oxygen (O). How is it poss

lara31 [8.8K]

Answer:

See explanation

Explanation:

A carbohydrate is formed from carbon, hydrogen and oxygen. These three elements are combined in every carbohydrate.

Even though carbohydrates are composed of only these three atoms, the number of atoms of these elements in each carbohydrate as well as the spatial arrangement of these atoms in each carbohydrate is not the same.

This means that different carbohydrates contain different number of carbon, oxygen and hydrogen atoms which are arranged in different ways in space. This gives room for the existence of many different types of carbohydrates all consisting of carbon, hydrogen and oxygen atoms.

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2 years ago

What wind direction change usually occurs as a cold front moves through an area?

Yanka [14]

Answer:

northern winds

Explanation:

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3 years ago

Read 2 more answers

HEYYY FAM IS THIS RIGHT

Otrada [13]

Answer: A reversible reaction is a reaction that takes place in back and front directions. If the reaction were to reach equilibrium, the rate of forward direction would be equal to that of the reverse reaction.

Explanation:

Reversible reactions :

These are the reaction in which reactants reacts to give product and products reacts to give reactants as a product in return.

$A+B\leftrightharpoons C+D$

In above equation, 'A' and 'B' are reacting together to give 'C' and 'D', as products and vice-versa.
When the above reaction reaches equilibrium the rate of forward and backward reaction becomes equal.

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2 years ago