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3 years ago

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42.5 grams of an unknown substance is heated to 105.0 degrees Celsius and then placed into a calorimeter containing 110.0 grams

of water at 24.2 degrees Celsius. If the final temperature reached in the calorimeter is 32.4 degrees Celsius, what is the specific heat of the unknown substance?
Show or explain the work needed to solve this problem, and remember that the specific heat capacity of water is 4.18 J/(° C × g).

1 answer:

iVinArrow [24]3 years ago

5 0

Answer:

The specific heat of the unknown substance is 1.22 J/g.°C.

Explanation:

Knowing that:

Heat lost by substance (Qc) = Heat gained by the water (Qw) ,

<em>- (Qc) = (Qw).</em>

<em></em>

We can calculate the amount of heat (Qw) gained by water using the relation:

Qw = m.c.ΔT,

where, Qw is the amount of heat released to water (Q = ??? J).

m is the mass of water (m = 110.0 g).

c is the specific heat capacity of solution (c = 4.18 J/g.°C).

ΔT is the difference in T (ΔT = final temperature - initial temperature = 32.4°C - 24.2°C = 8.2°C).

<em>∴ Q = m.c.ΔT = </em>(110.0 g)(4.18 J/g.°C)(8.2°C) = <em>3770.36 J.</em>

Now, the amount of heat lost by the substance <em>(Qc) = - 3770.36 J.</em>

(Qc) = m.c.ΔT,

where, Qc is the amount of heat lost by substance (Qc = - 3770.36 J).

m is the mass of water (m = 42.5 g).

c is the specific heat capacity of solution (c = ??? J/g.°C).

ΔT is the difference in T (ΔT = final temperature - initial temperature = 32.4°C - 105.0°C = -72.6°C).

∴ (- 3770.36 J) = (42.5 g)(c)(-72.6°C).

∴ c = (- 3770.36 J)/(42.5 g)(-72.6°C) = 1.222 J/g.°C.

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The atmospheric pressure on the surface of Venus is 6.84X10^4. Calculate the atmospheric pressure in atm and torr. Round each of

quester [9]

Answer:

0.675 atm

513 Torr

Explanation:

Given is that, the atmospheric pressure on the surface of Venus is

6.84 X 10⁴ Pa.

1 atm (atmospheric pressure) is equal to 101325 pascal (Pa).

To convert divide the pressure value by 101325.

Pressure in atm = $\frac{6.84 \times 10^{4} }{101325}$

= 0.675055 atm

Rounding it off to 3 significant digits: 0.675 atm

Now, one Torr is 133.322 Pa. For conversion, divide the pressure value by 133.322.

Pressure in Torr = $\frac{6.84 \times 10^{4} }{133.322}$

=513.04219 Torr

Rounding it off to 3 significant digits: 513 Torr

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3 years ago

How many moles of liquid water must freeze to remove 100 kJ of heat? (ΔHf = –334 J/<br> g.

Juliette [100K]

First figure out how many grams must freeze and then convert the grams to moles.
<span>Hf = -334 J/g. Convert this to KJ/g by dividing by 1000. (There are 1000 Joules in a kJ). </span>
<span>Hf = -334 J/g ÷ 1000 J/kj = -0.334 kJ/g </span>
<span>Now, divide 100 kJ by -0.334 kJ/g (see how the units are lining up?) </span>
<span>100 kJ ÷ -0.334 kJ/g = 299 g </span>
<span>Now convert this to moles by dividing by the molecular weight of water (18.0g/mole). </span>
<span>299 ÷ 18.0 = 16.6 moles </span>

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3 years ago

Boron has primarily two isotopes, one with an atomic mass of 11.0 amu and another with an atomic mass of 10.0 amu. If the abunda

Masja [62]

Answer:

The atomic mass of the boron atom would be <em>10.135</em>

Explanation:

This is generally known as relative atomic mass.

Relative atomic mass or atomic weight is a physical quantity defined as the ratio of the average mass of atoms of a chemical element in a given sample to the atomic mass of 1/12 of the mass of a carbon-12 atom. Since both quantities in the ratio are masses, the resulting value is dimensionless; hence the value is said to be relative and does not have a unit.

<em>Note that the relative atomic mass of atoms is not always a whole number because of it being isotopic in nature.</em>

<em>Divide each abundance by 100 then multiply by atomic mass</em>
<em>Do that for each isotope, then add the two result. Thus</em>

Relative atomic mass of Boron = (18.5/100 x 11) + (81/100 x 10)

= 2.035 + 8.1

= 10.135

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3 years ago

Identify the main purpose of the Periodic Table. *

saw5 [17]

The periodic table is one of the most important tools in the history of chemistry. It describes the atomic properties of every known chemical element in a concise format, including the atomic number, atomic mass and relationships between the elements. Elements with similar chemical properties are arranged in columns in the periodic table.

The table thus is a quick reference as to what elements may behave the same chemically or which may have similar weights or atomic structures.

Hope this answer helps you

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3 years ago

Name two compounds with more exothermic lattice energies than scandium oxide and justify your choice.

N76 [4]

Answer:

1 . $Al_2O_3$

2. $TiO_2$

Explanation:

The more stable the ionic compound, the more is it lattice energy.

The more the charge on the cation and the anion, the greater is the lattice energy.
The less the size of the cation and the anion, the greater is the lattice energy.

Scandium oxide ( $Sc_2O_3$ ) is an oxide in which $Sc^{3+}$ behaves as cation and $O^{2-}$ behaves as anion.

The compounds which has higher lattice energy than scandium oxide are:

1 . $Al_2O_3$

This is because the charge are same on the cation and the anion as in the case of the Scandium oxide but the size of the cation $Al^{3+}$ is smaller than $Sc^{3+}$ . Thus, this corresponds to higher lattice energy.

2. $TiO_2$

This is because the charge on the cation $Ti^{4+}$ is greater than that of $Sc^{3+}$ and also the size of the cation $Ti^{4+}$ is smaller than $Sc^{3+}$ . Thus, this corresponds to higher lattice energy.

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3 years ago