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3 years ago

What is the second most abundant element in stars? A. helium B. iron C. hydrogen D. oxygen

1 answer:

8 0

The abundance of a chemical element is a measure of the occurrence of the element relative to all other elements in a given environment. Abundance is measured in one of three ways: by the mass-fraction (the same as weight fraction); by the mole-fraction (fraction of atoms by numerical count, or sometimes fraction of molecules in gases); or by the volume-fraction. Volume-fraction is a common abundance measure in mixed gases such as planetary atmospheres, and is similar in value to molecular mole-fraction for gas mixtures at relatively low densities and pressures, and ideal gas mixtures. Most abundance values in this article are given as mass-fractions.

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How many boxes of B would be required to make 30 grams of C?

Mashutka [201]

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3 0

3 years ago

At T = 250 °C the reaction PCl5(g) PCl3(g) + Cl2(g) has an equilibrium constant in terms of pressures Kp = 2.15. (a) Suppose the

Ganezh [65]

Answer:

To the right

Explanation:

Step 1: Given data

Partial pressure of PCl₅ (pPCl₅) = 0.548 atm

Partial pressure of PCl₃ (pCl₃) = 0.780 atm

Partial pressure of Cl₂ (pCl₂) = 0.780 atm

Step 2: Write the balanced equation

PCl₅(g) ⇄ PCl₃(g) + Cl₂(g)

Step 3: Calculate the pressure reaction quotient

$Q_p = \frac{pPCl_3 \times pCl_2 }{pPCl_5} = \frac{0.780 \times 0.780 }{0.548} =1.11$

Step 4: Determine whether the reaction proceeds to the right or to the left as equilibrium is approached

Since Qp < Kp, the reaction will proceed to the right to attain the equilibrium.

7 0

3 years ago

Give the number of protons, neutrons and electrons in 99Tc

miss Akunina [59]

Explanation:

Tc - 99 is technetium 99.

It is a radioactive element that decays spontaneously. It has a half-life of 211,000 years and decays to stable ruthenium.

On the periodic table, it has an atomic number of 43;

Mass number = 99

Atomic number = number of protons = number of electrons in atom

Number of protons in Tc is 43

electron is 43

Mass number = number of protons + number of neutrons

Number of neutrons = mass number - number of protons = 99-43 = 56

learn more:

Atomic number brainly.com/question/2057656

#learnwithBrainly

5 0

3 years ago

What important processes in your body depend on mitosis

PilotLPTM [1.2K]

Mitosis makes new cells and replaces the cells that are old, lost or damaged

3 0

3 years ago

When a 12.8 g sample of KCL dissolves in 75.0 g of water in a calorimeter the temp. drops from 31 Celsius to 21.6 Celsius. Calcu

Delicious77 [7]

Answer:

Step 1: Calculate qsur (the surrounding is

usually the water)

qsur = ? J

m = 75.0 g water

c = 4.184 J/g

ΔT = (Tfinal- Tinitial)= (21.6 – 31.0) = -9.4 oC

qsur = m · c · (ΔT)

qsur = (75.0g) (4.184 J/g

oC) (-9.4 oC)

qsur = - 2949.72 J

First, using the information we know that we

must solve for qsur, which is the water. We know

the mass for water, 75.0g, the specific heat of

the water, 4.184 j/g

c, and the change in

temperature, 21.6-31.0 = -9.4 oC. Plugging it

into the equation, we solve for qsur.

Step 2: Calculate qsys qsys = - (qsur)

qsys = - (- 2949.72 J)

qsys = + 2949.72

In this case, the qsur is negative, which means

that the water lost energy. Where did it go? It

went to the system. Thus, the energy of the

system is negative, opposite, the energy of the

surrounding.

Step 3: Calculate moles of the substance

that is the system

Given: 12.8 g KCl

Mol system = (g system given)

(molar mass of system)

Mol system = (12.8 g KCl)

(39.10g + 35.45g)

Mol system = 12.8 g KCl

74.55 g

Mol system = 0.172

Here, we solve for the mol in the system by

using the molar mass of the material in the

system.

Step 4: Calculate ΔH ΔH = q sys .

Mol system

ΔH= + 2949.72 J

0.172 mol

ΔH= +17179.81 J/mol or +1.72 x 104

J/mol

i hope this helps

7 0

4 years ago