Which of the following statements about semi-empirical methods are true: It can be used for static molecules but not for reactions in which bonds are forming or breaking. It combines a theoretically sound model of bonding with some experimentally determined parameters. It can determine precisely both the location and the energy of bonding electrons. It is good at predicting structural properties that arise from subtle interactions of orbitals.
Answer:
The true statement about semi-empirical methods is:
It combines a theoretically sound model of bonding with some experimentally determined parameters.
Explanation:
Semi-empirical methods are theoretical assumptions combined with experimental data to improve computational performance. In modern computational chemistry, semi-empirical methods play important roles. The methods offer the advantage of a substantial reduction in computational time. They also increase one's ability to carry out calculations for large molecules. However, with these methods, there is the added loss of the variational principle because one can obtain a total energy that is below the true total energy. Again, semi-empirical methods have limited applicability because the methods apply to molecules with parameterized elements. Semi-empirical methods may supply spurious results, especially since the molecular systems may be different from those used for parameterizations.
Please help me thanks so much!?!?!?
Answer:
Lighting the stove and cooking the meat are both chemical changes.
Explanation:
Both fire and cooking are chemical changes.
Answer:
the second one
Explanation:
Why reaction of lead with dilute acid Cannot liberate hydrogen
Answer:
Copper does not reacts with dilute sulphuric acid, liberating hydrogen because copper is lower in the electromotive series than hydrogen. ... The metals above hydrogen in the activity series react with dilute sulphuric acid and dilute hydrochloric acid to liberate hydrogen.
Which of the following contains a polyatomic ion?
sodium iodide
carbon monoxide
Iron II oxide
ammonium chloride
Answer:
i think its oxide not too sure
Answer:
Its should be ammonium chloride.
A picture to help you with another question like this
Dale is speaking to a group of students about the importance of extracurricular activities. He provides specific scenarios to show the audience how the information presented will affected them directly. Dale is fulfilling which goal of informational speaking?
to enhance understanding
to be heard
to maintain interest
to be remembered
How many cells are a result of Meiosis?
Answer:
2
Explanation:
Cells divide and reproduce in two ways, mitosis and meiosis. Mitosis results in two identical daughter cells, whereas meiosis results in four sex cells.
Write a balanced chemical equation for the reaction of aqueous solutions of lead(II) nitrate and potassium iodide
to produce solid lead (II) iodi de and aqueous potassium nitrate.
Help pleaseee
Answer: Pb(NO3)2(aq) + 2KI(aq) —> PbI2(s) + 2KNO3(aq)
Explanation:
Three resonance structures of the given anion are possible. One is given, but it is incomplete. Complete the given structure by adding nonbonding electrons and formal charges. Draw the two remaining resonance structures (in any order), including nonbonding electrons and formal charges. Omit curved arrows.
Answer:
Explanation:
The missing incomplete resonance structure is attached in the image below. From there, we can see the addition of the nonbonding electrons and its' formal charge which makes the resonance structure a complete resonance structure. The others two resonance structure that can be derived from the complete structure is also shown in the image. Out of these three structures, the structure that contributes most to the hybrid is the structure with the negative charge on the oxygen.
A brown dye has a percent composition of 62.41% C, 5.24% H, and 32.36% N by mass with a molar mass of 346.40 g/mol. Determine the molecular formula of the dye
The molecular formula : C₁₈H₁₈N₈
Further explanationGiven
62.41% C, 5.24% H, and 32.36% N
Required
The molecular formula
Solution
mol ratio
C : 62.41/12.0096 = 5.1967
H : 5.24/1.00784 = 5.1992
N : 32.36/14.0067 = 2.310
Divide by 2.310(smallest)
C : 5.1967/2.31=2.25
H : 5.1992/2.31 = 2.25
N : 2.31/2.31 = 1
Multiplied by 4
C : H : N = 9 : 9 : 4
The empirical formula : C₉H₉N₄
(C₉H₉N₄)n=346.40 g/mol
(12.0096 x 9 + 1.00784 x 9 + 14.0067 x 4)n=346.4
(108.0864+9.07056+56.0268)n=346.4
(173.184)n=346.4
n=2
The molecular formula : C₁₈H₁₈N₈
Why is this image a good model for the Law of Conservation of Mass?
Answer:
The Law of Conservation of Mass states that mass is neither created nor destroyed in chemical reactions. Since the number and type of atoms in the reactant side of the chemical equation are the same as on the product side, the Law of Conservation of Mass has been demonstrated.
Explanation:
In the answer.
The two main postulates that was given by Antoine Lavoisier are, oxygen play an important role in combustion and the other is mass of the reactant and product is conserved. Therefore, the given image is a good model for the Law of Conservation of Mass.
What is law of conservation of mass?According to Law of conservation of mass, mass can neither be created nor be destroyed. Mass can only be transformed from one form to another. The law of conservation of mass was given by Antoine Lavoisier.
Every reaction in nature follow the law given by Antoine Lavoisier that is mass is always conserved. Another postulated that was given by Antoine Lavoisier is the role of oxygen in combustion reaction. Combustion can not happen without presence of oxygen.
The image is a good model for the Law of Conservation of Mass as number and type of atoms on the reactant side and product side are the same.
Therefore, the given image is a good model for the Law of Conservation of Mass.
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Sally does the work in 2.3 hours and Pete does 2.5
What is the amount of heat required to complete MELT a 200 gram sample of H2O(s)
Answer:
66800 J
Explanation:
From the question given above, the following data were obtained:
Mass (m) = 200 g
Heat (Q) required =?
The heat required to melt the 200 g sample of water can be obtained as:
Mass (m) = 200 g
Latent heat of water (L) = 334 J/g
Heat (Q) required =?
Q = mL
Q = 200 × 334
Q = 66800 J
Thus, 66800 J of heat energy is required to melt the sample of water.
Answer:
66800 J
Explanation:
How many molecules are there in 42gms of Na?
What is the maximum mass of ammonia (NH3) that can be produced from the synthesis reaction of 781 g of nitrogen and 656 g hydrogen?
HINT: You will need to write a balanced chemical equation and perform 2 calculations before you can determine the answers.
What is the difference between stored energy and usable energy
answer:
In biology, the energy that is stored in the bonds between compounds is termed as the chemical energy. This chemical energy is released and converted into different forms according to the functions of the body.
Potential energy can be described as the energy that is stored in an object. In physics, the energy that an object possesses while at rest is termed as the potential energy.
The energy that can be used during work is termed as the kinetic energy. In physics, kinetic energy can be described as the energy that an object possesses while in motion.
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Answer: The stored energy is termed as potential energy while the working energy is termed as kinetic energy. The electricity used in our homes is also a form of energy because it is a form of usable power. The places from which the different energies are obtained are known as energy sources.
Classify the following compounds as binary ionic, ternary ionic, or molecular.
Answer:bro u already have an answer why are you asking?
Explanation:
What is the function of the chloroplast? A. Breaks down sugar to make energy B. To hold the cell together C. To make animals green D. Uses sunlight to create glucose (sugar)
Answer:
D. Uses sunlight to create glucose (sugar)
Explanation:
The function of the chloroplast is that it uses sunlight to create glucose.
The chloroplast allows for light to be trapped which is used for the synthesis of glucose from carbon dioxide and water.
The chloroplast is a rich in a pigment called the chlorophyll. This chlorophyll is a green pigment which allows for the trapping of solar energy
This solar energy is used to carryout the photosynthetic reaction.
Match each term to its description. (3 points)
Excess reactant
Theoretical Yield
Limiting Reactant
1. Reactant that can produce more of
the product
2. Reactant that can produce a lesser
amount of the product
3. Amount of product predicted to be
produced by the given reactants
Answer:
1. B 2. C 3. A
Explanation:
I just took it
Limiting reactant is the reactant the produces the least amount of the product.
In a chemical reaction, the reactant that is in least supply is the limiting reactant while the reactant that is more than required is the excess reactant.
To match each term with its description, we have;
Excess reactant - Reactant that can produce more ofthe product
Limiting Reactant - Reactant that can produce a lesseramount of the product
Theoretical Yield - Amount of product predicted to beproduced by the given reactants
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Gluons carry
a
the weak force
b
gravity
c
Bosons
d
the strong force
e
electromagnetic force
Answer:
the answer is d
hope this helpssss
4. What is the percent by mass of tungsten in the calcium tungstate compound CaWO3, commonly
called scheelite?
Answer: 67.4%
Explanation:
Ca 40.8
W. 183.8
O. 16.00
CaWO3 272.6
W = 183.8/272.6 = 0.674
67.4% percent by mass of tungsten in the calcium tungstate compound CaWO3, commonly called scheelite.
What are calcium tungstate screens?The 200 Speed Blue Emitting Calcium Tungstate Screen is the most commonly used Non-Rare Earth intensifying screen. With a faster speed than Detail or Medium speed screens, the Hi-Plus Intensifying Screen provides an efficient balance between the time patients are exposed during x-rays and image quality and detail.
Who introduced calcium tungstate?It was also used in radium paint in the same fashion as was zinc sulfide, and Thomas Edison invented a fluoroscope with a calcium tungstate-coated screen, making the images six times brighter than those with barium platinocyanide; the latter chemical allowed Röntgen to discover X-rays in early November 1895.
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Given:
BO3 + 3Mg → 3MgO + B
1. How many moles of Mg are required if 2 moles of B are produced?
Answer:
6moles of Mg
Explanation:
The reaction expression is given as:
BO₃ + 3Mg → 3MgO + B
Given:
Number of moles of B produced = 2 moles
Unknown:
Number of moles of Mg required = ?
Solution:
From the balanced reaction expression:
1 mole of B is produced from 3 moles of Mg
2 moles of B will be produced from 2 x 3 = 6moles of Mg
A desert that contains plants and animals that have been there a long time is
an example of
which section from the article most emphasizes the role of technological development in the discovery of cells
Answer:
B. The microscope paved the way
Explanation:
This section from the article, "History of the Cell: Discovering the Cell", that emphasizes the role of technological development in the discovery of cells, is the subheading, "The microscope paved the way". In this subheading, the author narrated how Robert Hooke improved the existing microscope, and was able to discover the cell through it.
Further improvement of the simple microscope by Antonie van Leeuwenhoek led to the discovery of bacteria and protozoa.
Define degree of hardness of water? Mention different units.
Answer:
Degree of hardness is defined as the number of parts of calcium carbonate or equivalent to various calcium and magnesium salts present in a million parts of water by mass.
Explanation:
General guidelines for classification of waters are: 0 to 60 mg/L (milligrams per liter) as calcium carbonate is classified as soft; 61 to 120 mg/L as moderately hard; 121 to 180 mg/L as hard; and more than 180 mg/L as very hard. Lime scale buildup inside a water pipe
Units: mg/l , ppm , kg/[tex]m^{3}[/tex] , ppb , g/L
If I dilute 334.75 mL of 1.28 M lithium acetate solution to a volume of 822.18 ml, what
will the concentration of this solution be?
Answer:
C₂ = 0.52 M
Explanation:
Given data:
Initial volume = 334.75 mL
Initial concentration = 1.28 M
Final volume = 822.18 mL
Final concentration = ?
Solution:
C₁V ₁ = C₂V₂
By putting values,
1.28 M×334.75 mL = C₂×822.18 mL
C₂ = 1.28 M×334.75 mL / 822.18 mL
C₂ = 428.48 M.mL / 822.18 mL
C₂ = 0.52 M
According to bond energy tables, the triple bond of N2 is 946 kJ/mol while the bond of I2 is 151 kJ/mol. Based on simple chemical ideas about what molecular properties lead to activation energies, it is reasonable to expect that the reaction of H with N2 will have a higher activation energy than the reaction of H with I2.
1. Yes, I2 is heavier than N2.
2. No, bond energies do not matter much; lone pairs are crucial.
3. Yes, in both cases the reactant bond must be stretched by collisions and more energy is required for the stronger bond.
4. Yes, in both cases the reactant bond must be broken before the H can bond.
5. No, activation energies have nothing to do with bond energies.
Answer:
Yes, in both cases the reactant bond must be broken before the H can bond.
Explanation:
Let us remind ourselves of the basics of the collision theory. According to this theory, chemical reaction occurs because of the collision of particles of substances in a chemical reaction system.
This means that the bond between reactants must first be broken and new bonds formed in products. Activation energy is the minimum energy required for a reaction to occur. This energy goes into the rearrangement of reactant bonds to enable them to recombine and form products.
Since the N2 bond energy is far higher than the I2 bond energy, a greater degree of energy is needed overcome the energy barrier in the reaction of H2 with N2 compared to the reaction of H2 and I2 . Therefore, the activation energy for the reaction of H2 and N2 is much higher than the activation energy for the reaction of H2 with I2.
Why do organisms eat food? Be sure to explain your answer.
Answer:
Organisms need to take food to get energy and perform life processes. A living organism undergoes many life processes like nutrition, respiration, digestion, transportation, excretion, circulation of blood, and reproduction. To perform all these life processes the organism needs energy and nutrients.
Explanation:
nnastarannnn his idea
Please help with whatever this is and go in number order
definition of solubility
(science)
Answer:
th relative ability of a solute to devolve into a solvent
Which of the following choices is not evidence supporting the theory of plate tectonics?
Answer:
B
Explanation: