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3 years ago

When a substance melts it is said to go through all of the following except:

Chemistry

2 answers:

-Dominant- [34]3 years ago

7 0

The answer is C, chemical change

Alex Ar [27]3 years ago

4 0

C. Chemical change because it doesn’t change it chemical makeup but it will change temps it’s physical appearance and phase change or change of state

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The term _____ describes a substance that can act as both an acid and a base.

telo118 [61]

The term amphoteric describes a substance that can act as both an acid and a base.

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3 years ago

Some athletes have as little as 3.0% body fat. If such a person has a body mass of 67 kg , how many pounds of body fat does that

Elanso [62]

Data:
mass = 67 Kg → 147.71 pounds

Solving:

$\frac{3}{100}*147.71 = \frac{443.13}{100} \approx \boxed{4.43\:pounds\:of\:body\:fat}\end{array}}\qquad\quad\checkmark$

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3 years ago

5 atoms Pb to mol Pb

jek_recluse [69]

Answer:

0,83 x 10-²³ mol

Explanation:

n=N/Na

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3 years ago

A common radio wavelength observed coming from astronomical objects is 21 cm. What temperature is associated with this radiation

qaws [65]

Answer:

The temperature associated with this radiation is 0.014K.

Explanation:

If we assume that the astronomical object behaves as a black body, the relation between its wavelength and temperature is given by Wien's displacement law.

$\lambda_{max}=\frac{b}{T}$

where,

λmax is the wavelength at the peak of emission

b is Wien's displacement constant (2.89×10⁻³ m⋅K)

T is the absolute temperature

For a wavelength of 21 cm,

$T=\frac{b}{\lambda _{max} } = \frac{2.89 \times 10^{-3} m.K }{0.21m} =0.014K$

8 0

3 years ago

Hello, everyone!

marusya05 [52]

Answer: 27.09 ppm and 0.003 %.

First, for air pollutants, ppm refers to parts of steam or gas per million parts of contaminated air, which can be expressed as cm³ / m³. Therefore, we must find the volume of CO that represents 35 mg of this gas at a temperature of -30 ° C and a pressure of 0.92 atm.

Note: we consider 35 mg since this is the acceptable hourly average concentration of CO per cubic meter m³ of contaminated air established in the "National Ambient Air Quality Objectives". The volume of these 35 mg of gas will change according to the atmospheric conditions in which they are.

So, according to the law of ideal gases,

PV = nRT

where P, V, n and T are the pressure, volume, moles and temperature of the gas in question while R is the constant gas (0.082057 atm L / mol K)

The moles of CO will be,

n = 35 mg x $\frac{1 g}{1000 mg}$ x $\frac{1 mol}{28.01 g}$

→ n = 0.00125 mol

We clear V from the equation and substitute P = 0.92 atm and

T = -30 ° C + 273.15 K = 243.15 K

V = $\frac{0.00125 mol x 0.082057 \frac{atm L}{mol K} x 243 K}{0.92 atm}$

→ V = 0.0271 L

As 1000 cm³ = 1 L then,

V = 0.0271 L x $\frac{1000 cm^{3} }{1 L}$ = 27.09 cm³

Then the acceptable concentration c of CO in ppm is,

c = 27 cm³ / m³ = 27 ppm

To express this concentration in percent by volume we must consider that 1 000 000 cm³ = 1 m³ to convert 27.09 cm³ in m³ and multiply the result by 100%:

c = 27.09 $\frac{cm^{3} }{m^{3} }$ x $\frac{1 m^{3} }{1 000 000 cm^{3} }$ x 100%

c = 0.003 %

So, the acceptable concentration of CO if the temperature is -30 °C and pressure is 0.92 atm in ppm and as a percent by volume is 27.09 ppm and 0.003 %.

5 0

3 years ago