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3 years ago

What methods do scientists use to determine if a change was physical or chemical?

1 answer:

5 0

A physical change will not change the chemical make-up of the material. the change will not produce a new substance.

a chemical change will have a reaction that produces heat, light, a change in color, releases a gas, or rust

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A weather balloon is filled with helium that occupies a volume of 5.57 104 L at 0.995 atm and 32.0°C. After it is released, it r

Alchen [17]

6.52 × 10⁴ L. (3 sig. fig.)

<h3>Explanation</h3>

Helium is a noble gas. The interaction between two helium molecules is rather weak, which makes the gas rather "ideal."

Consider the ideal gas law:

$P\cdot V = n\cdot R\cdot T$ ,

where

$P$ is the pressure of the gas,
$V$ is the volume of the gas,
$n$ is the number of gas particles in the gas,
$R$ is the ideal gas constant, and
$T$ is the absolute temperature of the gas in degrees Kelvins.

The question is asking for the final volume $V$ of the gas. Rearrange the ideal gas equation for volume:

$V = \dfrac{n \cdot R \cdot T}{P}$ .

Both the temperature of the gas, $T$ , and the pressure on the gas changed in this process. To find the new volume of the gas, change one variable at a time.

Start with the absolute temperature of the gas:

$T_0 = (32.0 + 273.15) \;\text{K} = 305.15\;\text{K}$ ,
$T_1 = (-14.5 + 273.15) \;\text{K} = 258.65\;\text{K}$ .

The volume of the gas is proportional to its temperature if both $n$ and $P$ stay constant.

$n$ won't change unless the balloon leaks, and
consider $P$ to be constant, for calculations that include $T$ .

$V_1 = V_0 \cdot \dfrac{T_1}{T_2} = 5.57\times 10^{4}\;\text{L}\times \dfrac{258.65\;\textbf{K}}{305.15\;\textbf{K}} = 4.72122\times 10^{4}\;\text{L}$ .

Now, keep the temperature at $T_1 =258.65\;\text{K}$ and change the pressure on the gas:

$P_1 = 0.995\;\text{atm}$ ,
$P_2 = 0.720\;\text{atm}$ .

The volume of the gas is proportional to the reciprocal of its absolute temperature $\dfrac{1}{T}$ if both $n$ and $T$ stays constant. In other words,

$V_2 = V_1 \cdot\dfrac{\dfrac{1}{P_2}}{\dfrac{1}{P_1}} = V_1\cdot\dfrac{P_1}{P_2} = 4.72122\times 10^{4}\;\text{L}\times\dfrac{0.995\;\text{atm}}{0.720\;\text{atm}}=6.52\times 10^{4}\;\text{L}$

(3 sig. fig. as in the question.).

See if you get the same result if you hold $T$ constant, change $P$ , and then move on to change $T$ .

6 0

2 years ago

Number of moles in 1.806*10^22 molecules of nitrogen

Fynjy0 [20]

Hi there!

• Avogadro's number = 6.023 × 10²³
• No.of molecules in N = 1.806 × 10²² [ Given ]

It's known that :-

Number of molecules = Moles × Avogadro's number

=> 1.806 × 10²² = Mol. × 6.023 × 10²³

=> Mole = $\dfrac {1.806 \cdot 10^{22} }{6.023 \cdot 10^{23} }$

=> Moles = 0.03 mol.

Hence, 0.03 mol. is th' required answer.

~ Hope it helps!

3 0

3 years ago

What could help a scientist determine the approximate age of the dinosaur age?

jeka57 [31]

Answer:

The ages of dinosaur fossils are determined by the layer of rock in which they are ... you can see the complete geologic column, how do scientists know it exists? ... laid down over 542 million years, for an average of 49,272 years per foot of rock. .... dinosaurs lived in shallow water because it would help support their weight

Explanation:

3 0

3 years ago

Read 2 more answers

Which organisms perform photosynthesis in their cells

balu736 [363]

A:Autotrophs
Explanation: Heterotrophs get their energy by eating Autotrophs. Not by photosynthesis.

3 0

2 years ago

Which of these did your answer include?

sveticcg [70]

The oxygen atom has a partial negative charge and the Hydrogen atoms have a partial positive charge

8 0

2 years ago