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2 years ago

What is a substance and what are the two types of substances?

Chemistry

2 answers:

vladimir2022 [97]2 years ago

8 0

Answer:

The two types of substances are elements and compounds.

Explanation:

A pure substance is one in which the composition is definitive and constant throughout, and that has distinct chemical properties. These substances are comprised of only one entity, not a mixture of two or more.

Elements are pure substances, assuming they are free of imperfections, because they are made of only one type of atom.

Compounds are also pure substances, like water, table salt, table sugar, etc. because they are comprised of one type of compound (H2O, NaCL, C6H1206,etc)

masha68 [24]2 years ago

6 0

A pure substance has a constant composition and cannot be separated into simpler substances by physical means. There are two types of pure substances: elements and compounds. Elements: are pure substances made up of only l type of atom. Atoms of the same element are identical in properties.

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Consider two processes: sublimation of I2(s) and melting of I2(s) (Note: the latter process can occur at the same temperature bu

AVprozaik [17]

Answer:

positive

Explanation:

Entropy -

In a system, the randomness is measured by the term entropy .

Randomness basically refers as a form of energy that can not be used for any work.

The change in entropy is given by amount heat per change in temperature.

When solid is converted to gas entropy increases,

As the molecules in solid state are tightly packed and has more force of attraction between the molecules, but as it is converted to gas, the force of attraction between the molecule decreases and hence entropy increases.

So,

The particles of the substance , if are tightly held by strong force of attraction will decrease the entropy ,

And

If the particles are loosely held , the entropy will increase , i.e. , positive entropy .

Similar with solid converting to liquid , the entropy will increases , i.e. , positive entropy .

Hence ,

The correct sign of entropy for both the process is positive .

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2 years ago

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_________ is the movement of materials across a cell membrane using cellular energy.

Airida [17]

Answer:

active transport

Explanation:

passive transport does not involve energy

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2 years ago

The Ka for formic acid (HCO2H) is 1.8 × 10-4. What is the pH of a 0.35 M aqueous solution of sodium formate (NaHCO2)?

anzhelika [568]

Answer:

9.36

Explanation:

Sodium formate is the conjugate base of formic acid.

Also,

$K_a\times K_b=K_w$

$K_b$ for sodium formate is $K_b=\frac {K_w}{K_a}$

Given that:

$K_a$ of formic acid = $1.8\times 10^{-4}$

And, $K_w=10^{-14}$

So,

$K_b=\frac {10^{-14}}{1.8\times 10^{-4}}$

$K_b=5.5556\times 10^{-11}$

Concentration = 0.35 M

HCOONa ⇒ Na⁺ + HCOO⁻

Consider the ICE take for the formate ion as:

HCOO⁻ + H₂O ⇄ HCOOH + OH⁻

At t=0 0.35 - -

At t =equilibrium (0.35-x) x x

The expression for dissociation constant of sodium formate is:

$K_{b}=\frac {[OH^-][HCOOH]}{[HCOO^-]}$

$5.5556\times 10^{-11}=\frac {x^2}{0.35-x}$

Solving for x, we get:

x = 0.44×10⁻⁵ M

pOH = -log[OH⁻] = -log(0.44×10⁻⁵) = 4.64

pH + pOH = 14

So,

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2 years ago

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Veronika [31]

I believe the answer is B??????????? Hope this helps

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omeli [17]

Answer:

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2 years ago