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3 years ago

In the symbol (4/2)He, the superscript 4 is the for helium, and the subscript 2 is the for helium.

2 answers:

5 0

The superscript 4 is the atomic mass for helium, and the subscript 2 is the atomic number for helium.
I hope that will help you.Let me know if need more help on this

VLD [36.1K]3 years ago

4 0

the given symbol is

⁴₂He

subscript for the element is the atomic number of the element

atomic number is the number of protons . atomic number is characteristic for the element

superscript is the mass number. mass number is the sum of protons and neutrons. mass number means the atomic mass.

therefore atomic number is 2 and mass number is 4

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Butane (C4 H10(g), Hf = –125.6 kJ/mol) reacts with oxygen to produce carbon dioxide (CO2 , Hf = –393.5 kJ/mol ) and water (H2 O,

WITCHER [35]

Answer: Enthalpy of combustion (per mole) of $C_4H_{10} (g)$ is -2657.5 kJ

Explanation:

The chemical equation for the combustion of butane follows:

$2C_4H_{10}(g)+4O_2(g)\rightarrow 8CO_2(g)+10H_2O(g)$

The equation for the enthalpy change of the above reaction is:

$\Delta H^o_{rxn}=[(8\times \Delta H^o_f_{CO_2(g)})+(10\times \Delta H^o_f_{H_2O(g)})]-[(1\times \Delta H^o_f_{C_4H_{10}(g)})+(4\times \Delta H^o_f_{O_2(g)})]$

We are given:

$\Delta H^o_f_{(C_4H_{10}(g))}=-125.6kJ/mol\\\Delta H^o_f_{(H_2O(g))}=-241.82kJ/mol\\\Delta H^o_f_{(O_2(g))}=0kJ/mol\\\Delta H^o_f_{(CO_2(g))}=-393.5kJ/mol\\\Delta H^o_{rxn}=?$

Putting values in above equation, we get:

$\Delta H^o_{rxn}=[(8\times -393.5)+(10\times -241.82)]-[(2\times -125.6)+(4\times 0)]\\\\\Delta H^o_{rxn}=-5315kJ$

Enthalpy of combustion (per mole) of $C_4H_{10} (g)$ is -2657.5 kJ

6 0

2 years ago

What does iron do for the human body(two paragraphs)

Nitella [24]

Answer:

Hey mate....

Explanation:

This is ur answer.....

Iron is an essential element for blood production. About 70 percent of your body's iron is found in the red blood cells of your blood called hemoglobin and in muscle cells called myoglobin. Hemoglobin is essential for transferring oxygen in your blood from the lungs to the tissues. Myoglobin, in muscle cells, accepts, stores, transports and releases oxygen. About 6 percent of body iron is a component of certain proteins, essential for respiration and energy metabolism, and as a component of enzymes involved in the synthesis of collagen and some neurotransmitters. Iron also is needed for proper immune function. About 25 percent of the iron in the body is stored as ferritin, found in cells and circulates in the blood. The average adult male has about 1,000 mg of stored iron (enough for about three years), whereas women on average have only about 300 mg (enough for about six months). When iron intake is chronically low, stores can become depleted, decreasing hemoglobin levels. When iron stores are exhausted, the condition is called iron depletion. Further decreases may be called iron-deficient erythropoiesis and still further decreases produce iron deficiency anemia.

Hope it helps!

Brainliest pls!

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6 0

2 years ago

On the basis of the information above, a buffer with a pH = 9 can best be made by using

telo118 [61]

Answer:

D H2PO4– + HPO42–

Explanation:

The acid dissociation constant for $\mathbf{H_3PO_4 , H_2PO^{-}_4 , HPO_4^{2-}}$ are $\mathbf{7\times 10^{-3}, \ \ 8\times 10^{-8} ,\ \ 5\times 10^{-13}}$ respectively.

$\mathbf{pka (H_3PO_4) = -log (7\times 10^{-3} )=2.2}$

$\mathbf{pka (H_2PO_4^-) = -log (8\times 10^{-8} )=7.1}$

$\mathbf{pka (HPO_4^{2-}) = -log (5\times 10^{-13} )=12.3}$

The reason while option D is the best answer is that, the value of pKa for both

$\mathbf{H_2PO^{-}_4 ,\ \& \ HPO_4^{2-}}$ lies on either side of the desired pH of the buffer. This implies that one is slightly over and the other is slightly under.

Using Henderson-Hasselbach equation:

$\mathbf{pH = pKa + log \Big( \dfrac{HPO_4^{2-}}{H_2PO_4^-} \Big)}$

3 0

2 years ago

Construct an argument for or against the immediate introduction of fuel-cell cars. Include likely points of objection from those

ryzh [129]

Answer:

Explanation:

Fuel Cell Cars are the vehicles built to run on hydrogen gas rather than running on the hydrocarbon.

Hydrocarbons are the organic compounds which are derived mostly from the crude oil. They are usually composed of Hydrogen and Carbon.

Fuel cell cars are much more better than the regular vehicles running on hydrocarbon in so many ways especially environmentally.

Listed below are some of the advantages of fuel cell cars over the regular vehicles

Fuel cells have a higher efficiency than diesel or gas engines.

Most fuel cells operate silently, compared to internal combustion engines. They are therefore ideally suited for use within buildings such as hospitals.

Fuel cells can eliminate pollution caused by burning fossil fuels; for hydrogen fuelled fuel cells, the only by-product at point of use is water.

If the hydrogen comes from the electrolysis of water driven by renewable energy, then using fuel cells eliminates greenhouse gases over the whole cycle.

Fuel cells do not need conventional fuels such as oil or gas and can therefore reduce economic dependence on oil producing countries, creating greater energy security for the user nation.

Since hydrogen can be produced anywhere where there is water and a source of power, generation of fuel can be distributed and does not have to be grid-dependent.

The use of stationary fuel cells to generate power at the point of use allows for a decentralised power grid that is potentially more stable.

8 0

3 years ago

Read 2 more answers

Extension: Cedric has been in the hospital for 15 weeks, how many minutes is that? Use

almond37 [142]

Answer:

151200 minutes.

Explanation:

From the question given above, the following data were obtained:

Time (in week) = 15 weeks

Time (in min) =?

Next, we shall convert 15 weeks to days. This can be obtained as follow:

1 week = 7 days

Therefore,

15 weeks = 15 weeks × 7 days / 1 week

15 weeks = 105 days

Next, we shall convert 105 days to hours. This can be obtained as follow:

1 day = 24 h

Therefore,

105 days = 105 days × 24 h / 1 day

105 days = 2520 h

Finally, we shall convert 2520 h to mins. This can be obtained as follow:

1 h = 60 mins

Therefore,

2520 h = 2520 h × 60 mins / 1 h

2520 h = 151200 mins

Thus, 15 weeks is equivalent to 151200 minutes.

6 0

2 years ago