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3 years ago

Which process is a chemical change? breaking of glass formation of frost magnetization of an iron nail loss of atmospheric ozone

Chemistry

2 answers:

Elenna [48]3 years ago

3 0

The answer is "D" loss of atmospheric ozone

Anna35 [415]3 years ago

3 0

Answer:

The answer is loss of atmospheric ozone

Explanation:

There are two types of change in chemistry, they are physical and chemical change.

Physical changes are characterized by the following

they are easily reversible
no new substance is formed
they cannot be represented by a chemical equation

Chemical changes are characterized by the following

they are not easily reversible
new substances are mostly formed
they are usually represented by chemical equations

When a glass breaks, the broken parts are still glasses, no new particle is formed and we can't represent the process with a chemical equation

Frost are just iced-water crystals that are formed on objects in an open environment. They are formed from water and as such they reverse back to water (no new substance is formed) when the temperature increases and the process cannot be represented by a chemical equation.

The nail that has been attracted by a magnet can be easily removed and no new substance is formed in the process. The process of magnetization cannot be represented by a chemical equation

The loss of atmospheric ozone is a chemical process because ozone cannot be easily formed/broken as this requires several processes. During depletion of ozone (O3), oxygen gas (O2) is formed hence a new substance is formed and this process can be represented with the use of chemical equation. Let's take the depletion of ozone by chlorofluorocarbon (CFCs) as an example.

When CFCs are broken by sunlight, they break up into there components and chlorine (Cl) is released and when that occurs, the following reaction takes place after the break up

Cl + O3 ⇒ ClO + O2

we can see from the chemical equation above that depletion of atmospheric ozone is a chemical process

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A titration of 25.0 mL of a solution of the weak base aniline, C6H5NH2, requires 25.67 mL of 0.175 M HCl to reach the equivalenc

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Answer:

a. 0.180M of C₆H₅NH₂

b. 0.0887M C₆H₅NH₃⁺

c. pH = 2.83

Explanation:

a. Based in the chemical equation:

C₆H₅NH₂(aq) + HCl(aq) → C₆H₅NH₃⁺(aq) + Cl⁻(aq)

<em>1 mole of aniline reacts per mole of HCl</em>

Moles required to reach equivalence point are:

Moles HCl = 0.02567L ₓ (0.175mol / L) = 4.492x10⁻³ moles HCl = moles C₆H₅NH₂

As the original solution had a volume of 25.0mL = 0.0250L:

4.492x10⁻³ moles C₆H₅NH₂ / 0.0250L = 0.180M of C₆H₅NH₂

b. At equivalence point, moles of C₆H₅NH₃⁺ are equal to initial moles of C₆H₅NH₂, that is 4.492x10⁻³ moles

But now, volume is 25.0mL + 25.67mL = 50.67mL = 0.05067L. Thus, molar concentration of C₆H₅NH₃⁺ is:

[C₆H₅NH₃⁺] = 4.492x10⁻³ moles / 0.05067L = 0.0887M C₆H₅NH₃⁺

c. At equivalence point you have just 0.0887M C₆H₅NH₃⁺ in solution. C₆H₅NH₃⁺ has as equilibrium in water:

C₆H₅NH₃⁺(aq) + H₂O(l) → C₆H₅NH₂ + H₃O⁺

Where Ka = Kw / Kb = 1x10⁻¹⁴ / 4.0x10⁻¹⁰ =

When the system reaches equilibrium, molar concentrations are:

[C₆H₅NH₃⁺] = 0.0887M - X

[C₆H₅NH₂] = X

[H₃O⁺] = X

Replacing in Ka formula:

2.5x10⁻⁵ = [X] [X] / [0.0887M - X]

2.2175x10⁻⁶ - 2.5x10⁻⁵X = X²

0 = X² + 2.5x10⁻⁵X - 2.2175x10⁻⁶

Solving for X:

X = -0.0015 → False solution. There is no negative concentrations.

X = 0.001477 → Right solution.

As [H₃O⁺] = X, [H₃O⁺] = 0.001477

Knowing pH = -log [H₃O⁺]

pH = -log 0.001477

7 0

3 years ago

Nitrogen dioxide and water react to form nitric acid and nitrogen monoxide, like this:

posledela

Answer: The value of the equilibrium constant Kc for this reaction is 3.72

Explanation:

Equilibrium concentration of $HNO_3$ = $\frac{15.5g}{63g/mol\times 9.5L}=0.026M$

Equilibrium concentration of $NO$ = $\frac{16.6g}{30g/mol\times 9.5L}=0.058M$

Equilibrium concentration of $NO_2$ = $\frac{22.5g}{46g/mol\times 9.5L}=0.051M$

Equilibrium concentration of $H_2O$ = $\frac{189.0g}{18g/mol\times 9.5L}=1.10M$

Equilibrium constant is defined as the ratio of concentration of products to the concentration of reactants each raised to the power their stoichiometric ratios. It is expressed as $K_c$

For the given chemical reaction:

$2HNO_3(aq)+NO(g)\rightarrow 3NO_2(g)+H_2O(l)$

The expression for $K_c$ is written as:

$K_c=\frac{[NO_2]^3\times [H_2O]^1}{[HNO_3]^2\times [NO]^1}$

$K_c=\frac{(0.051)^3\times (1.10)^1}{(0.026)^2\times (0.058)^1}$

$K_c=3.72$

Thus the value of the equilibrium constant Kc for this reaction is 3.72

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