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3 years ago

8

The EPA scientist measures the pH level in one area of a river to be lower than normal and writes that a pollutant must have bee

n discharged from a factory just upstream. This is an example of

2 answers:

shutvik [7]3 years ago

4 0

Its an example of inference.

HACTEHA [7]3 years ago

3 0

Answer:

INFERENCE.

next question answer:

A LINE GRAPH.

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Which statement about AHf is true?

Pachacha [2.7K]

Answer:

<u><em>It is positive when the bonds of the product store more energy than those of the reactants.</em></u>

Explanation:

The <em>standard enthalpy of formation</em>, <em>ΔHf</em>, is defined as the energy required to form 1 mole of a substance from its contituent elements under standard conditions of pressure and temperature.

Then, per defintion, when the elements are already at their standard states, there is not energy involved to form them from that very state; this is, the standard enthalpy of formation of the elements in their standard states is zero.

It is not zero for the compounds in its standard state, because energy should be released or absorbed to form the compounds from their consituent elements. Thus, the first choice is false.

When the bonds of the products store more energy than the those of the reactants, the difference is:

ΔHf = ΔHf products - ΔHf reactants > 0, meaning that ΔHf is positive. Hence, the second statement is true.

Third is false because forming the compounds may require to use (absorb) or release (produce) energy, which means that ΔHf could be positive or negative.

Fourth statement is false, because the standard state of many elements is not liquid. For example, it is required to supply energy to iron to make it liquid. Thus, the enthalpy of formation of iron in liquid state is not zero.

3 0

3 years ago

Choose all that apply. Nitrogen has an atomic number of 7. Its atomic mass is 14. Nitrogen has

Goshia [24]

The atomic number of calculated as number of protons + number of neutrons. The number of protons are the same as atomic number. This implies that Nitrogen has seven protons. To get the the number of neutron we minus atomic mass from number of protons
that is 14-7=7 neutrons

6 0

3 years ago

Licemer1 [7]

Answer:

79 protons.

Explanation:

8 0

2 years ago

What is common to nuclear fission?

ipn [44]

Answer:

235 U ( the isotope of uranium with mass number 235) and 239Pu(the isotope of plutonium with mass number 239

Explanation:

mmmmmmmmm

5 0

3 years ago

According to the experimental procedure of Experiment F1, 135 microliters of acetophenone (120.15 g/mol, 1.03 g/mL) was reacted

Delicious77 [7]

Answer: The theoretical yield of 4-nitrochalcone is, $2.13\times 10^2$

Explanation : Given,

Volume of acetophenone = 135 microliters = 135 × 10⁻⁶ L = 0.135 mL

conversion used : (1 microliter = 10⁻⁶ L) and (1 L = 1000 mL)

Density of acetophenone = 1.03 g/mL

Mass of acetophenone = Density × Volume = 1.03 g/mL × 0.135 mL = 0.139 g

Mass of 4-nitrobenzaldehyde = 127 mg = 0.127 g

Conversion used : (1 mg = 0.001 g)

First we have to calculate the moles of acetophenone and 4-nitrobenzaldehyde

$\text{Moles of acetophenone}=\frac{\text{Given mass acetophenone}}{\text{Molar mass acetophenone}}$

$\text{Moles of acetophenone}=\frac{0.139g}{120.15g/mol}=0.00116mol$

and,

$\text{Moles of 4-nitrobenzaldehyde}=\frac{\text{Given mass 4-nitrobenzaldehyde}}{\text{Molar mass 4-nitrobenzaldehyde}}$

$\text{Moles of 4-nitrobenzaldehyde}=\frac{0.127g}{151.12g/mol}=0.000840mol$

Now we have to calculate the limiting and excess reagent.

The balanced chemical equation is:

$C_8H_8O+C_7H_5NO_3\rightarrow C_{15}H_{11}NO_3$

From the balanced reaction we conclude that

As, 1 mole of 4-nitrobenzaldehyde react with 1 mole of acetophenone

So, 0.000840 mole of 4-nitrobenzaldehyde react with 0.000840 mole of acetophenone

From this we conclude that, acetophenone is an excess reagent because the given moles are greater than the required moles and 4-nitrobenzaldehyde is a limiting reagent and it limits the formation of product.

Now we have to calculate the moles of 4-nitrochalcone

From the reaction, we conclude that

As, 1 mole of 4-nitrobenzaldehyde react to give 1 mole of 4-nitrochalcone

So, 0.000840 mole of 4-nitrobenzaldehyde react to give 0.000840 mole of 4-nitrochalcone

Now we have to calculate the mass of 4-nitrochalcone

$\text{ Mass of 4-nitrochalcone}=\text{ Moles of 4-nitrochalcone}\times \text{ Molar mass of 4-nitrochalcone}$

Molar mass of 4-nitrochalcone = 253.25 g/mole

$\text{ Mass of 4-nitrochalcone}=(0.000840moles)\times (253.25g/mole)=0.21273g=212.73mg=2.13\times 10^2mg$

(1 g = 1000 g)

Therefore, the theoretical yield of 4-nitrochalcone is, $2.13\times 10^2mg$

4 0

3 years ago