A block of ice is placed on a hot sidewalk. The ice melts because.

The changes are classified as follows:

1: Chemical change -  The addition of the water to quicklime

2: Physical change - The melting of candle wax

3: Physical change -  The change in colour of zinc oxide from white to yellow and vice versa during heating and after cooling, respectively

4: Physical change- The dissolution of common salt

5: Chemical change - The hardening of cement by the absorption of carbon (Iv) oxide​

1: The addition of water to quicklime (slaking of lime) is a chemical change. It involves a chemical reaction between calcium oxide (quicklime) and water to form calcium hydroxide (slaked lime). This reaction is exothermic and produces heat.

2: The melting of candle wax is a physical change. It involves a phase transition from a solid state to a liquid state due to the application of heat. The chemical composition of the wax remains unchanged during this process.

3: The change in color of zinc oxide from white to yellow and vice versa during heating and cooling is a physical change. It is a reversible process caused by the alteration of the crystal structure of zinc oxide. The change in color is due to the absorption or release of energy during the heating and cooling processes, respectively.

4: The dissolution of common salt (sodium chloride) is a physical change. It involves the separation of ionic bonds between sodium and chloride ions in the solid salt and their subsequent dispersal in water. The chemical composition of the salt remains the same; it simply forms a homogeneous mixture with water.

5: The hardening of cement by the absorption of carbon dioxide (CO2) is a chemical change. It involves a chemical reaction known as carbonation, where carbon dioxide reacts with the calcium hydroxide in cement to form calcium carbonate. This reaction leads to the formation of new chemical compounds and a change in the structure and properties of the cement, resulting in its hardening or curing process.

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Answer:

In a physical change the appearance or form of the matter changes but the kind of matter in the substance does not. However in a chemical change, the kind of matter changes and at least one new substance with new properties is formed.

Explanation:

Answer:The first thing you need to do is calculate the molar mass of C4H10.

Explanation:

Answer:

5 is the answer

Explanation:

I hope it helps you!

Answer:

#1 exothermic

Answer:

do u take links bcs I can give u one with the answer?

The approximate initial boiling point of Magnesium chloride solution has been 102.33 degree Celsius.

The pure water has boiling point 100 degree Celsius. With the addition of the solvent, the boiling point has been increased. The change in the boiling point (\(\Delta T_b\)) has been given as:

\(\Delta T_b=i.K_b.b\)

Where, i has been the van't Hoff factor

\(K_b\) has been the ebullioscopic constant

b has been the molality of the sample

The dissolution of magnesium chloride in water has been given as:

\(\rm MgCl_2\;(aq)\;\rightarrow\;Mg^2^+\;+\;2\;Cl^-\)

The i has been the amount of molecules that has been formed by the dissociation of 1 molecule. The dissociation of Magnesium chloride has been resulted in the 1 Mg and 2 Cl. Thus, the i for Magnesium chloride has been 3.

The molality (m) of the solution has been given as:

\(m = \dfrac{m_s_o_l_u_t_e}{mwt}\;\times\;\dfrac{1000}{m_s_o_l_v_e_n_t}\)

Where, \(m_s_o_l_u_t_e=285\;\text {g}\\m_s_o_l_v_e_n_t=2\;\text{kg}\\mwt=95.211\;\text{g/mol}\)

Substituting the values, molality of the Magnesium chloride solution (b) can be given as:

\(b=\dfrac{285}{95.211}\;\times\;\dfrac{1}{2}\;\text{m}\\b=1.49\;\text{m}\)

The molality of the solution has been 1.49 m.

Substituting the values for change in temperature:

\(\Delta T_b=3\;\times\;0.52\;\times\;1.49\;^\circ \text C\\\Delta T_b=2.33\;^\circ \text C\)

The rise in boiling temperature with the addition of 285 g of Magnesium chloride has been 2.33 \(\rm ^\circ C\). Since, the initial temperature for pure solvent has been 100 degree Celsius.

The initial temperature of Magnesium chloride solution has been the sum of two. Thus:

\(\text {Initial temperature}=100^\circ \text C\;+\;2.33\;^\circ \text C\\\rm Initial\;temperature=102.33\;^\circ C\)

The initial temperature of magnesium chloride solution has been 102.33 degree Celsius.

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The mass of water produced if the percent yield of the reaction is 72% is 16.2g.

Mass of acetylene = 40.0 grams

Mass of oxygen = 40.0 grams

Percent yield of the reaction = 72%

The balanced chemical equation is : 2 C2H2(g) + 5 O2(g) → 4 CO2(g) + 2 H2O(g)

From the balanced chemical equation, it is clear that 2 moles of acetylene reacts with 5 moles of oxygen to form 2 moles of water.

To find out limiting reagent

Moles of acetylene = Given mass of acetylene / molar mass of acetylene

                                 = 40.0 g / 26 g/mol = 1.54 moles

Moles of oxygen = Given mass of oxygen / molar mass of oxygen

                                = 40.0 g / 32 g/mol = 1.25 moles

The limiting reactant is oxygen because its number of moles is less than acetylene. Oxygen will react with 1.25 moles of acetylene present and form CO2 and H2O.

According to the balanced equation, the stoichiometric ratio of C2H2 to H2O is 2:2, meaning that for every 2 moles of C2H2, 2 moles of H2O are produced.

Since the stoichiometry is 1:1, the moles of water produced will be the same as the moles of acetylene used.

The number of moles of H2O produced 1.25 moles.

The mass of H2O produced = Number of moles of H2O × Molar mass of H2O

Mass of H2O produced = 1.25 × 18 = 22.5 g

Given percent yield = 72%

The actual yield can be calculated as follows;

Percent yield = Actual yield / Theoretical yield × 100

72% = Actual yield / 22.5 g × 100

Actual yield = 22.5 g× 72 / 100 =16.2 g

Thus, the mass of water produced if the percent yield of the reaction is 72% is 16.2g.

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Option (a) is correct. If a reaction is at equilibrium and we will increase the volume of the reaction then the Reaction will shift to the right in the direction of product.

The Reaction is,

2H2S(g) + 3O2(g) ----> 2H2O(g) + 2SO2(g) a)

According to Le Chatelier's principle, if a dynamic equilibrium is disturbed by changing the conditions the position of equilibrium shifts to counteract the change to reestablish an equilibrium. If a chemical reaction is at equilibrium and experiences a change in pressure, temperature or concentration of products or reactants, the equilibrium shifts in the opposite direction to offset the change. A change in one of the variables that describe a system at equilibrium produces a shift in the position of the equilibrium that counteracts the effect of this change.

We are increasing pressure here. Reaction will try to decrease the pressure. Hence it will move in a direction which have lesser gaseous molecules. Here product has less gaseous molecule. So equilibrium will move to right. Equilibrium moves to product side.

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The molar solubility of Mg(OH)2 in pure water is calculated to be approximately 1.34 x 10⁻⁶ M. In the presence of 8.68 x 10⁻² M MgCl2, the molar solubility of Mg(OH)2 decreases to approximately 1.34 x 10⁻⁶ - 8.68 x 10⁻² M.

In the presence of 3.65 x 10⁻² M KOH(aq), the molar solubility of Mg(OH)2 increases to approximately 1.34 x 10⁻⁶ + 3.65 x 10⁻² M. The solubility of a compound, represented by its molar solubility, depends on the presence of other ions in the solution. In pure water, Mg(OH)2 dissociates into Mg²⁺ and 2OH⁻ ions. The solubility product expression for Mg(OH)2 is given by Ksp = [Mg²⁺][OH⁻]², and since the concentration of Mg²⁺ is equal to the concentration of OH⁻, we can represent the molar solubility of Mg(OH)2 as x M. Substituting these values into the Ksp expression, we get x * (2x)² = 1.8 x 10⁻¹¹. Solving this equation yields x ≈ 1.34 x 10⁻⁶ M as the molar solubility of Mg(OH)2 in pure water.

In the presence of MgCl2, the concentration of Mg²⁺ ions increases due to the dissociation of MgCl2. However, since Mg(OH)2 is a sparingly soluble salt, the increase in Mg²⁺ concentration does not significantly affect the solubility of Mg(OH)2. Therefore, the molar solubility remains approximately the same as in pure water.

In the presence of KOH(aq), the concentration of OH⁻ ions increases. This increase in OH⁻ ions shifts the equilibrium towards the dissociation of Mg(OH)2, leading to an increase in its molar solubility. Therefore, the molar solubility of Mg(OH)2 increases by approximately 3.65 x 10⁻² M in the presence of 3.65 x 10⁻² M KOH(aq).

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Answer:

83.82 g of magnesium ions.

Explanation:

We want to determine the mass of magnesium ions in 155.0 grams of magnesium phosphide (Mg₃P₂).

We can convert from grams of Mg₃P₂ to moles of Mg₃P₂, moles of Mg₃P₂ to moles of Mg, and moles of Mg to grams of Mg.

Find the molecular weight (molar mass) of magnesium phosphide:

\(\displaystyle \begin{aligned}\text{MW}_\text{Mg$_3$P$_2$} &= \left(3(24.31)+2(30.97)\right) \text{ g/mol} \\ \\ &= (72.93 + 61.94) \text{ g/mol} \\ \\ &= 134.87 \text{ g/mol}\end{aligned}\)

The molecular weight of magnesium is 24.31 g/mol*.

From the chemical formula, we can see that there are three moles of magnesium for every one mole of magnesium phosphide.

Hence, multiply initial amount with known ratios:

\(\displaystyle \begin{aligned} &155.0 \text{ g Mg$_3$P$_2$} \cdot \frac{1 \text{ mol Mg$_3$P$_2$}}{134.87\text{ g/mol}} \cdot \frac{3\text{ mol [Mg$^{2+}$]}}{1 \text{ mol Mg$_3$P$_2$}}\cdot \frac{24.31 \text{ g [Mg$^{2+}$]}}{1 \text{ mol [Mg$^{2+}$]}}\\ \\ & = 83.82 \text{ g [Mg$^{2+}$]}\end{aligned}\)

In conclusion, there are 83.82 grams of magnesium ions in 155.0 grams of magnesium phosphide.

*Because the magnesium ions in magnesium phosphide have two less electrons, its molecular weight will indeed be lower. However, due to the extremely small size of an electron (1/2000th of a proton), the difference in mass is insignificant.

Explanation:

because they have more protons

Answer:C12: 0.487 m

Explanation:

Answer:

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Zebra

Sing

Yoga

Gaming

Cooking

The missing component of the nuclear equation is 4 2He

The following data were obtained from the question:

The missing component, X of the nuclear equation can be obtained as illustrated below:

230 90Th --> 226 88Ra + a bX

230 = 226 + a

Collect like terms

a = 230 - 226

a = 4

90 = 88 + c

Collect like terms

c = 90 - 88

c = 2

a cX => 4 2X => 4 2He

Thus, the complete equation is:

230 90Th --> 226 88Ra + 4 2He

Therefore, the missing component, of the equation is 4 2He

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Answer: To find the wavelength of the photons emitted by hydrogen atoms when they undergo n = 4 to n = 2 transitions, we can use the Rydberg formula:

1/λ = R_H * (1/n1² - 1/n2²)
Where λ is the wavelength, R_H is the Rydberg constant for hydrogen (approximately 1.097 x 10^7 m^-1), n1 and n2 are the initial and final energy levels, respectively.

Explanation:

The formula used to determine the wavelength of light is known as the Rydberg formula. The energy of an electron changes when it transitions from one atomic orbit to another. The photon of light is produced when the electron transitions from a high-energy orbit to a lower-energy state. Additionally, the photon of light is absorbed by the atom when the electron transitions from a low energy to a higher energy state.

In this case, n1 = 2 and n2 = 4. Plugging the values into the formula, we get:

1/λ = (1.097 x 10^7) * (1/2² - 1/4²)

1/λ = (1.097 x 10^7) * (1/4 - 1/16)

1/λ = (1.097 x 10^7) * (12/64)

λ = 1 / (1.097 x 10^7 * 12/64)

λ ≈ 4.86 x 10^-7 m

Converting meters to nanometers (1 m = 1 x 10^9 nm):

λ ≈ 486 nm

The wavelength of the photons emitted by hydrogen atoms when they undergo n = 4 to n = 2 transitions is approximately 486 nm. This radiation occurs in the visible region of the electromagnetic spectrum.

Answer: The wavelength of the photons emitted by hydrogen atoms when they undergo n = 4 to n = 2 transitions is approximately 486 nm, and this radiation occurs in the visible region of the electromagnetic spectrum (option d).

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Answer:

Explanation:

The answer is C Enthaply and entropy because temperature plays a big role in reactions

Answer:

c

Explanation:

a p e x :)

If you mix 100 g of ice at 0.00°c with 60 g of water at 60 °c, then 60 g of ice has melted. The water is cooled to 0.00°c as some of the ice melts. The ice also melted.

Ice has a melting point of 0°C, or 273K. Tungsten, which is used to create the filaments in light bulbs, is the chemical element with the highest melting point (3410°C). The temperature of the system does not rise during the melting process until after the melting point has been reached, even after all the ice has melted. Water is the primary component of the Earth's hydrosphere and the fluids of all known living things. It is an inorganic chemical with the chemical formula H2O(water) and is transparent, tasteless, odourless, and almost colourless.

H = MS(deltaT) (deltaT)

H = 100*4.184*(60-0)

H = 25104J

Now, the amount of heat needed to melt ice to 0 degrees Celsius is given by the formula delta H = 100*2.108 = 421.6J m = 24682.4/40.7*10^3 = 0.606g.

Ice melted to a total of 0.606g.

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Answer:

The earlier bog bodies that were discovered in the 1600s might have not been preserved properly due to a lack of knowledge on how to preserve them or a lack of awareness of their significance. It is also possible that they might have decayed and decomposed over time and not survived till the present day. However, the bog bodies found after the late 1800s were preserved and studied extensively due to the increasing awareness and understanding of their historical and archaeological significance.

Explanation:

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The ion in seawater that serves as a buffer is HCO₃⁻ (bicarbonate ion). Option D is correct.

Seawater is a complex mixture of various dissolved salts and ions, including sodium (Na⁺), chloride (Cl⁻), calcium (Ca²⁺), and bicarbonate (HCO₃⁻).

A buffer is the solution which resists changes in pH when an acid or base is added to it. It consists of a weak acid and its conjugate base, or a weak base and its conjugate acid. In the case of seawater, the bicarbonate ion (HCO₃⁻) acts as a buffer.

HCO₃⁻ can act as both a weak acid and its conjugate base. It can donate a proton (H⁺) to act as an acid or accept a proton to act as a base. This ability to accept or donate protons helps maintain the pH of seawater within a relatively narrow range.

When an acid is added to seawater, the bicarbonate ion (HCO₃⁻) can accept the excess protons and convert into carbonic acid (H₂CO₃). This conversion helps to reduce the increase in acidity and prevent a drastic decrease in pH.

Therefore, HCO₃⁻ in seawater acts as a buffer, helping to stabilize and maintain the pH of the water despite the addition of acids or bases.

Hence, D. is the correct option.

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a. The chemical formula for this hydrate is determined by comparing the change in mass before and after heating. The initial mass of the hydrated salt (0.821 g) minus the mass of the dried salt (0.448 g) gives the mass of water lost during heating, which is 0.373 g. To find the molar ratio between the anhydrous salt and water, we divide the mass of the anhydrous salt by its molar mass (NiCl2).

Assuming all the water is lost and the anhydrous salt is left, the molar mass of NiCl2 is 129.6 g/mol. So, (0.448 g / 129.6 g/mol) gives us the number of moles of NiCl2.

Using the molar ratio between the anhydrous salt and water, we can determine the number of moles of water lost during heating, which is (0.373 g / 18.02 g/mol). Simplifying the ratio between the anhydrous salt and water gives us the chemical formula for this hydrate, which is NiCl2 · 6H2O.

b. The IUPAC name for this hydrate is determined based on the number of water molecules associated with the anhydrous salt. In this case, since there are 6 water molecules attached to each NiCl2, the IUPAC name for this hydrate is nickel(II) chloride hexahydrate.

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The folate cycle is directly involved in the metabolism of methionine and the synthesis of purine and pyrimidine nucleotides.

The folate cycle plays a crucial role in several metabolic pathways, including the metabolism of methionine and the synthesis of purine and pyrimidine nucleotides.

Methionine, an essential amino acid, is converted to S-adenosylmethionine (SAM) through a series of reactions involving folate as a coenzyme. SAM is a methyl donor involved in numerous methylation reactions, including DNA methylation and protein methylation.

Folate is also necessary for the synthesis of purine and pyrimidine nucleotides, which are essential for DNA and RNA synthesis. The folate cycle provides the necessary one-carbon units required for these processes, making it directly involved in these amino acid metabolic pathways.

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Answer:

Explanation:

The new volume of the balloon can be found by using the formula for Boyle's law which is

\(P_1V_1 = P_2V_2\)

Since we are finding the new volume

\(V_2 = \frac{P_1V_1}{P_2} \\\)

From the question we have

\(V_2 = \frac{1 \times 1}{0.4} = \frac{1}{0.4} \\ = 2.5\)

We have the final answer as

Hope this helps you

We see that the RMSD is much smaller than the bond length. This is expected, as the nuclei of the atoms in a molecule oscillate around their equilibrium positions with small amplitudes, even at room temperature.

The root-mean-square displacement (RMSD) of the nuclei in a molecule is given by the following formula:

RMSD = √(3RT/2k)

where R is the gas constant, T is the temperature in Kelvin, and k is the force constant of the bond in N/m.

The force constant of the bond in C₁₂O₁₆ can be calculated using the equilibrium bond length (r_e) and the reduced mass (mu) of the molecule:

k = mu x (2pi x c)² / (r_e)²

where c is the speed of light.

The reduced mass (mu) of C₁₂O₁₆ is:

mu = m_C x m_O / (m_C + m_O)

where m_C and m_O are the masses of carbon and oxygen, respectively. From the periodic table, we have:

m_C = 12.01 g/mol

m_O = 16.00 g/mol

Therefore:

mu = 12.01 g/mol x 16.00 g/mol / (12.01 g/mol + 16.00 g/mol) = 6.646 g/mol

The force constant of the bond can be calculated using the equation:

k = mu x (2pi x c)² / (r_e)²

where c is the speed of light:

c = 2.998 x 10⁸ m/s

Substituting the values, we get:

k = 6.646 g/mol x (2pi x 2.998 x 10⁸ m/s)² / (112.832 pm)²

k = 1.939 x 10³ N/m

Assuming the temperature is room temperature (298 K), the RMSD of the nuclei is:

RMSD = √(3RT/2k) = √(3 x 8.314 J/mol K x 298 K / (2 x 1.939 x 10³ N/m))

RMSD = 6.02 x 10⁻¹² m

Comparing the RMSD with the equilibrium bond length

(112.832 pm = 1.12832 x 10⁻¹⁰ m), we see that the RMSD is much smaller than the bond length. This is expected, as the nuclei of the atoms in a molecule oscillate around their equilibrium positions with small amplitudes, even at room temperature.

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Ionic and covalent bonds differ in terms of bond formation, electron sharing, and the types of elements involved. When the pH goes from 7 to 4, the concentration of H+ ions increases, leading to a decrease in OH- concentration. This shift indicates a more acidic solution.

Ionic bonds occur between a metal and a non-metal, where electrons are transferred from the metal to the non-metal, resulting in the formation of charged ions. Covalent bonds, on the other hand, occur between non-metal atoms that share electrons to achieve a stable electron configuration.

When the pH goes from 7 to 4, it indicates a decrease in the pH value, shifting towards acidity. The pH scale is logarithmic, meaning that each unit change represents a tenfold difference in H+ ion concentration. As the pH decreases, the concentration of H+ ions increases, while the concentration of OH- ions decreases. This is because the concentration of H+ and OH- ions in water is inversely proportional, following the equation: [H+][OH-] = 1.0 x \(10^{-14}\) at 25°C. Therefore, when the pH decreases, the concentration of H+ ions increases, leading to a decrease in OH- concentration.

Based on the pH table, a pH of 7 represents a neutral solution, where the concentration of H+ ions is equal to the concentration of OH- ions. As the pH decreases to 4, the concentration of H+ ions increases by a factor of 1,000, while the concentration of OH- ions decreases accordingly. This shift towards a higher H+ concentration indicates a more acidic solution.

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The half-life of a compound if 42% of a given sample of the compound decomposes in 60 min is 45.1 min (rounded to one decimal place).

In a first-order reaction, the rate of decomposition is directly proportional to the concentration of the reactant.

That is, the reaction rate (R) is proportional to the concentration (C) raised to the power of :

1.Rate of reaction = - dC/dt = kC

Where k is the rate constant and t is the time taken.

Therefore, the integrated form of the equation for first-order kinetics is:

ln [C]t - ln [C]0 = - kt

Where [C]t and [C]0 are the concentrations at time t and at time zero respectively, k is the rate constant, and t is the time taken for the reaction to proceed.

The half-life of a reaction is the time taken for half of the reactant to be consumed,

i.e., when [C]t = [C]0 / 2.

Substituting these values into the integrated equation, we have:

ln ([C]0 / 2) - ln [C]0 = - kt12 ln 1/2 = - kt1/2 = (ln 2) / k

Now we can use the half-life equation to find k: 60 min

= t1/2

= (ln 2) / kk

= 0.0116 min-1

Now that we know the rate constant, we can use the integrated equation to find the half-life of the reaction for 42% decomposition.

Using 0.42[C]0 and solving for t, we get:

t = 45.1 min

Therefore, the half-life of the reaction for 42% decomposition is 45.1 min.

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Answer: Option (b) is the correct answer.

Explanation:

It is known that,

                   pH + pOH = 14

So, pOH = 14 - pH

As the given pH is 9.3. Hence, pOH for the given solution will be calculated as follows.

          pOH = 14 - 9.3

                   = 4.7

Therefore, pOH of the given solution is 4.7.

Answer:1.A ____ is like a recipe for a chemical substance. (valence, formula, subscript, coefficient)

2

The____ in a formula tells the number of atoms of each element present. (valence, formula, subscript, coefficient)

Explanation:

1.A ____ is like a recipe for a chemical substance. (valence, formula, subscript, coefficient)

2

The____ in a formula tells the number of atoms of each element present. (valence, formula, subscript, coefficient)

A formula is like a recipe for a chemical substance.

The coefficient in a formula tells the number of atoms of each element present.

A chemical compound may be defined as a type of chemical substance that is mainly composed of many similar molecules that contain atoms of more than one chemical element. These atoms are typically held together by chemical bonds.

The formula of any chemical substance will significantly rely on the number and nature of the chemical element which is present in it. While the coefficient in the formula simply conveys the number of a particular atom present of each element present in the chemical formula.

Therefore, both incomplete statement is appropriately filled with a particular word to make the most valid and accurate sense.

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Answer: at the same rate with what please?

Explanation:

Answer: Option B; It traps light energy and converts it into chemical energy.