Which of these is a model that
represents valence electrons in
an atom as dots around the
element's chemical symbol?

Answer:

hmmm?what?

Explanation:

ayusin mo flece:>

Answer:

c

no need to thank me okay

Answer:

Mass number (A) is the number of nucleons (proton and neutron) present in a atom.

Explanation:

electrons don't cout since they are thousandth's of the mass of protons or neutrons

If the salt water is heated, the water turns into steam and the salt remains because the water has a lower boiling point than the salt.

The  following points can be considered:

The process involved when salt water is heated:

Therefore, the answer is water has a lower boiling point than salt.

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Answer:

Loss of protons and electrons in plutonium 240 decay is not an example of an everyday reaction

Answer: 2,25 mol

Explanation: 2Al + 3CuSO4 → Al2(SO4)3 + 3Cu

                    1,5 mol                                                       (1,5*3)/2 mol = 2,25 mol

Answer:

Draw the predominant product(s) of the following reactions including stereochemistry when it is appropriate.

CH3CH2 C C CH3 H2O/H2SO4/HgSO4

Explanation:

The given compound is: pent-2-yne.

When it reacts with water, in presence of sulphuric acid and mercuric sulphate then a ketone is formed as shown below:

This reaction is an example of nucleophilic attack of water on carbon carbon triple bond.

The general mechanism of the reaction is hsown below:

Pent-2-yne reacts with water and form 3-pentanone.

The reaction is shown below:

Answer:

6, double

Explanation:

Hex- is a prefix for number 6.

Ene- is a suffix for a double bond.

Formula is (CH3)2CHCH2C(CH3)3 and the name is 2,2,4-trimethylpentane

Answer: The value for rate constant for a reaction is [tex]4.81\times 10^{-4} s^{-1}[/tex]

Explanation:

The integrated rate law equation for first-order kinetics:

[tex]k=\frac{2.303}{t}\log \frac{a}{a-x}[/tex] ......(1)

Let the initial concentration of reactant be 100 g

Given values:

a = initial concentration of reactant = 100 g

a - x = concentration of reactant left after time 't' = 25 % of a = 25 g

t = time period = 48 min = 2880 s       (Conversion factor: 1 min = 60 s)

Putting values in equation 1:

[tex]k=\frac{2.303}{2880s}\log (\frac{100}{25})\\\\k=4.81\times 10^{-4} s^{-1}[/tex]

Hence, the value for rate constant for a reaction is [tex]4.81\times 10^{-4} s^{-1}[/tex]

Answer:

2.42x10⁹ years is the age of the rock

Explanation:

The decay of an isotope follows the equation:

Ln[A] = -kt + Ln[A]₀

Where [A] is amount of isotope after time t, k is decay constant and [A]₀ is the initial amount of the isotope

To find decay constant from half-life:

k = ln2 / half-life

k = ln2 / 1.26x10⁹years

k = 5.501x10⁻¹⁰ years⁻¹

As in the reaction, K-40 produce Ar-40:

[A] = 0.359mmol

[A]₀ = 0.359mmol + 1.000mmol = 1.359mmol

Replacing:

Ln[0.359mmol] = -5.501x10⁻¹⁰ years⁻¹t + Ln[1.359mmol]

-1.3312 = -5.501x10⁻¹⁰ years⁻¹t

t = 2.42x10⁹ years is the age of the rock

Answer:

Examples of isotones include carbon-12, nitrogen-13 and oxygen-14. These atoms all have six neutrons and six, seven and eight protons respectively. A mnemonic that can be used to differentiate isotones from isotopes and isobars is as follows: same Z (number of protons) = isotopes.

An OH group attached to a hydrocarbon is called an alkyl group whereas hydroxide is a polyatomic ion with a charge of -1.

OH group is also called hydroxyl group. Alcohol is a type of organic compound that is characterized by one or more hydroxyl (―OH) groups attached to a carbon atom of an hydrocarbon chain so we can conclude that an OH group attached to a hydrocarbon is called an alkyl group whereas hydroxide is a polyatomic ion with a charge of -1.

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Answer:

1.62 g

Explanation:

Given that:

Concentration of HCN = 0.119 M

Assuming the ka 4.00 × 10⁻¹⁰

The pKa of  HCN (hydrocyanic acid)  = -log (Ka)

= - log ( 4.00 × 10⁻¹⁰)

= 9.398

pH of buffer = 8.809

Using Henderson Hasselbach equation:

[tex]pH = pKa + log \dfrac{[conjugate\ base ]}{acid}[/tex]

[tex]pH = pKa + log \dfrac{[CN^-]}{[HCN]}[/tex]

[tex]8.809 = 9.398 +log \dfrac{[CN^-]}{[HCN]}[/tex]

[tex]log \dfrac{[CN^-]}{[HCN]}= 8.809 - 9.398[/tex]

[tex]log \dfrac{[CN^-]}{[HCN]}= -0.589[/tex]

[tex]\dfrac{[CN^-]}{[HCN]}= 0.2576[/tex]

[CN^-] = 0.2576[HCN]

[CN^-] = 0.2756 (0.119) L

[CN^-] = 0.033 M

∴

The amount of NaCN (sodium cyanide) is calculated as follows:

[tex]= 1.00 L \times \dfrac{0.033 \ mol \ NacN }{1 \ L } \times \dfrac{49.01 \ g}{1 \ mol \ of \ NacN}[/tex]

= 1.62 g

Answer: The mass of [tex]CO_2[/tex] produced is 0.44 g

Explanation:

The number of moles is defined as the ratio of the mass of a substance to its molar mass.  The equation used is:

[tex]\text{Number of moles}=\frac{\text{Given mass}}{\text{Molar mass}}[/tex] ......(1)

Given mass of calcium carbonate = 10 g

Molar mass of calcium carbonate = 100 g/mol

Plugging values in equation 1:

[tex]\text{Moles of calcium carbonate}=\frac{10g}{100g/mol}=0.1 mol[/tex]

The formula used to calculate molarity:

[tex]\text{Molarity of solution}=\frac{\text{Moles of solute}\times 1000}{\text{Volume of solution (mL)}}[/tex] .....(2)

Molarity of HCl = [tex]0.2mol/dm^3=0.2mol/L[/tex]     (Conversion factor: [tex]1L=1dm^3[/tex]

Volume of solution = [tex]100cm^3=100mL[/tex]          (Conversion factor: [tex]1mL=1cm^3[/tex]

Putting values in equation 2, we get:

[tex]0.2=\frac{\text{Moles of HCl}\times 1000}{100}\\\\\text{Moles of HCl}=\frac{0.2\times 100}{1000}=0.02mol[/tex]

For the given chemical reaction:

[tex]CaCO_3(s)+2HCl(aq)\rightarrow CaCl_2(aq)+H_2O(l)+CO_2(g)[/tex]

By stoichiometry of the reaction:

If 2 moles of HCl reacts with 1 mole of calcium carbonate

So, 0.02 moles of HCl will react with = [tex]\frac{1}{2}\times 0.02=0.01mol[/tex] of calcium carbonate

As the given amount of calcium carbonate is more than the required amount. Thus, it is present in excess and is considered as an excess reagent.

Thus, HCl is considered a limiting reagent because it limits the formation of the product.

By the stoichiometry of the reaction:

If 2 moles of [tex]HCl[/tex] produces 1 mole of [tex]CO_2[/tex]

So, 0.02 moles of [tex]HCl[/tex] will produce = [tex]\frac{1}{2}\times 0.02=0.01mol[/tex] of [tex]CO_2[/tex]

We know, molar mass of [tex]CO_2[/tex] = 44 g/mol

Putting values in equation 1, we get:

[tex]\text{Mass of }CO_2=(0.01mol\times 44g/mol)=0.44g[/tex]

Hence, the mass of [tex]CO_2[/tex] produced is 0.44 g

Answer:

3.9g/cm3

Explanation:

Density ( d)=?

Mass(m)=27.3g

Volume (v)=7.0cm3

D=m÷v

D=27.3g÷7.0cm3

D=3.9g/cm3

Answer:

the scientific name of lion is

Panthera leo

With the help of hess's law:

ΔHf(MnO)=−248.9 kJ−12(272.0) kJ=−384.9 kJ(per mole) Δ H f ( M n O ) = − 248.9 k J − 1 2 ( 272.0 ) k J = − 384.9 k J ( p e r m o l e )

Hess's law of constant heat summation, also known simply as Hess' law, is a relationship in physical chemistry named after Germain Hess, a Swiss-born Russian chemist and physician who published it in 1840.

Moreover, hess's Law of Constant Heat Summation (or just Hess's Law) states that regardless of the multiple stages or steps of a reaction, the total enthalpy change for the reaction is the sum of all changes.

Therefore, hess' law is based on the state function character of enthalpy and the first law of thermodynamics. Energy (enthalpy) of a system (molecule) is a state function.

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Answer:

Explanation:

Diels-Alder reactions are cyclo-additional reactions between conjugated dienes and a dienophile (a substituted alkene compound for example acrylic acid) to produce a ring structure of cyclohexene compounds.

From the image attached below, we will see the reaction between 2,3-dimethylbuta-1,3-diene which is a conjugated diene with acrylic acid to produce a Diel-Alder adduct as the product.  From the reaction, a single new π-bond and two σ-bonds are produced.

Answer:

compounds are elements include an element and a compound

Explanation:

elements in the decomposition reaction is the substance that cannot be separated into simpler substances. Compounds, technically act as a reactant in the decomposition reaction, but since the reaction breakdown one substance into two or more, sometimes it exists in the product

Answer:

Ammonium hydroxide, NH₄OH

Magnesium hydroxide, Mg(OH)₂

Sodium hydroxide, NaOH

Lithium hydroxide, LiOH

Explanation:

A base is a substance which neutralizes acids to produce salt and water. Bases are hydroxide or oxides of metals. Bases may be soluble or insoluble in water. Bases generally have a bitter taste and turn red litmus paper or indicator red.

Alkalis are bases which are soluble in water. They form the hydroxide of the alkali metals or alkaline earth metals in solution and they ionize to produce hydroxide ions. They are slippery to touch and turn red litmus blue being bases.

Therefore, all alkalis are bases but not all bases are alkalis. Insoluble bases are not alkalis.

From the given chemical compounds the alkalis present in the list are:

Ammonium hydroxide, NH₄OH; since it is soluble in water and produces hydroxide ions

Magnesium hydroxide, Mg(OH)₂; since it is slightly soluble in water and produces hydroxide ions

Sodium hydroxide, NaOH; since it is soluble in water and produces hydroxide ions

Lithium hydroxide, LiOH; since it is soluble in water and produces hydroxide ions

CuO(copper oxide) is a base but not an alkali as it does not produce hydroxide ions.

Zn(OH)2 (zinc hydroxide) is amphoteric and is insoluble

MgO(magnesium oxide) is a base but not an alkali as it does not produce hydroxide ions.

Na2O(sodium oxide) is a base but not an alkali as it does not produce hydroxide ions.

CoO(cobalt oxide) is a base but not an alkali as it does not produce hydroxide ions.

Answer:

It is a colourless, odourless, tasteless gas that is the most plentiful element in Earth's atmosphere and is a constituent of all living matter.

Explanation:

Have a nice day :D

Answer:

Nitrogen is a gas

Explanation:

Hukkam aap bio image dekhona please and bataona ki kese lage

Answer:

Adding ammonium nitrate to water turns the mixture cold and is a good example of an endothermic chemical reaction!

Answer:

11) the difference in heat energies between products and reactants

12) enthalpy change

Explanation:

The heat of reaction is defined as that energy released or absorbed as chemical substances participate in a chemical reaction. It is a term used to denote the change in energy as reactants change into products.

Another name of heat of reaction is enthalpy of reaction. It is a state function since it depends on the initial and final states of the system.

Answer:

In an ionic bond, the elctrons are transferred. For example, NaCl has an ionic bond because Na loses an electron and the Cl atom gains the electron. However in a covalent bond, the electrons are shared equally. Covalent bonds usually occur between two nonmetals.

Explanation:

Answer :

Answer:

For A: The wavelength of the light is [tex]1.052\times 10^4nm[/tex]

For B: The number of photons per joule is [tex]2.063\times 10^{18}[/tex]

For C: The binding energy of a metal is 1.197 eV.

Explanation:

The equation used to calculate the energy of a photon follows:

[tex]E=\frac{hc}{\lambda}[/tex]            ......(1)

where,

E = energy of a photon

h = Planck's constant = [tex]6.626\times 10^{-34}J.s[/tex]

c = speed of light = [tex]3\times 10^{8}m/s[/tex]

[tex]\lambda[/tex] = wavelength

Given values:

E = [tex]1.89\times 10^{-20}J[/tex]

Putting values in equation 1, we get:

[tex]\lambda=\frac{(6.626\times 10^{-34}J.s)\times (3\times 10^8m/s)}{1.89\times 10^{-20}J}\\\\\lambda=1.052\times 10^{-5}m[/tex]

Converting the wavelength into nanometers, the conversion factor used is:

[tex]1m=10^9nm[/tex]

So, [tex]\lambda=1.052\times 10^{-5}m\times \frac{10^9nm}{1m}=1.052\times 10^4nm[/tex]

Hence, the wavelength of the light is [tex]1.052\times 10^4nm[/tex]

Given values:

[tex]\lambda=410nm=410\times 10^{-9}m[/tex]

Putting values in equation 1, we get:

[tex]E=\frac{(6.626\times 10^{-34}J.s)\times (3\times 10^8m/s)}{410\times 10^{-9}m}\\\\E=4.848\times 10^{-19}J[/tex]

To calculate the number of photons, we use the equation:

[tex]\text{Number of photons}=\frac{\text{Total energy}}{\text{Energy of a photon}}[/tex]

Total energy = 1 J

Energy of a photon = [tex]4.848\times 10^{-19}J[/tex]

Putting values in the above equation:

[tex]\text{Number of photons}=\frac{1J}{4.848\times 10^{-19}J}\\\\\text{Number of photons}=2.063\times 10^{18}[/tex]

Hence, the number of photons per joule is [tex]2.063\times 10^{18}[/tex]

To calculate the binding energy of a metal, we use the equation:

[tex]E=K+B[/tex]             .....(2)

E = Total energy

K = Kinetic energy of a photon

B = Binding energy of metal

Converting the energy from joules to eV, the conversion factor used is:

[tex]1eV=1.602\times 10^{-19}J[/tex]

Using the above conversion factor:

[tex]K=2.93\times 10^{-19}J=1.829eV\\\\E=4.848\times 10^{-19}J=3.026eV[/tex]

Putting values in equation 2:

[tex]B=(3.026-1.829)eV=1.197eV[/tex]

Hence, the binding energy of a metal is 1.197 eV.

Answer:

b

Explanation:

Answer:

B

Explanation: