Think fast! An element has 25 protons and 22 electrons. It has a charge of...

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Fudgin [204]

Answer:

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8 0

3 years ago

Which of the following is kept constant when using a bomb calorimeter?

trapecia [35]

Constant Volume Calorimetry, also know as bomb calorimetry, is used to measure the heat of a reaction while holding volume constant and resisting large amounts of pressure. Although these two aspects of bomb calorimetry make for accurate results, they also contribute to the difficulty of bomb calorimetry. In this module, the basic assembly of a bomb calorimeter will be addressed, as well as how bomb calorimetry relates to the heat of reaction and heat capacity and the calculations involved in regards to these two topics.

Introduction

Calorimetry is used to measure quantities of heat, and can be used to determine the heat of a reaction through experiments. Usually a coffee-cup calorimeter is used since it is simpler than a bomb calorimeter, but to measure the heat evolved in a combustion reaction, constant volume or bomb calorimetry is ideal. A constant volume calorimeter is also more accurate than a coffee-cup calorimeter, but it is more difficult to use since it requires a well-built reaction container that is able to withstand large amounts of pressure changes that happen in many chemical reactions.

Most serious calorimetry carried out in research laboratories involves the determination of heats of combustion ΔHcombustion" role="presentation" style="display: inline-table; font-style: normal; font-weight: normal; line-height: normal; font-size: 14.4px; text-indent: 0px; text-align: left; text-transform: none; letter-spacing: normal; word-spacing: normal; word-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; padding: 0px; margin: 0px; position: relative;">ΔHcombustionΔHcombustion, since these are essential to the determination of standard enthalpies of formation of the thousands of new compounds that are prepared and characterized each month. In a constant volume calorimeter, the system is sealed or isolated from its surroundings, and this accounts for why its volume is fixed and there is no volume-pressure work done. A bomb calorimeter structure consists of the following:

Steel bomb which contains the reactantsWater bath in which the bomb is submergedThermometerA motorized stirrerWire for ignition

is usually called a “bomb”, and the technique is known as bomb calorimetry

Another consequence of the constant-volume condition is that the heat released corresponds to qv , and thus to the internal energy change ΔUrather than to ΔH. The enthalpy change is calculated according to the formula

(1.1)ΔH=qv+ΔngRT" role="presentation" style="display: inline-table; font-style: normal; font-weight: normal; line-height: normal; font-size: 14.4px; text-indent: 0px; text-align: center; text-transform: none; letter-spacing: normal; word-spacing: normal; word-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; padding: 0px; margin: 0px; width: 10000em !important; position: relative;">ΔH=qv+ΔngRT(1.1)(1.1)ΔH=qv+ΔngRT

Δng" role="presentation" style="display: inline-table; font-style: normal; font-weight: normal; line-height: normal; font-size: 14.4px; text-indent: 0px; text-align: left; text-transform: none; letter-spacing: normal; word-spacing: normal; word-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; padding: 0px; margin: 0px; position: relative;">ΔngΔng is the change in the number of moles of gases in the reaction.

6 0

3 years ago

A plot of binding energy per nucleon Eb A versus the mass number (A) shows that nuclei with a small mass number have a small bin

Illusion [34]

Answer:

6He = 4.90 MeV/Nucleon

8Li = 5.18 MeV / Nucleon

62Ni = 8.82 MeV / Nucleon

115 In = 8.54 MeV / Nucleon

Explanation:

Our strategy here is to remember that when the mass of a given nuclei is calculated from the sum of the mass of its protons and neutrons, this mass is greater than the actual value . This is the mass defect.

Now this mass defect we can convert to energy by utilizing Einstein´s equation, E = mc².This is the binding energy.

For 6He with actual mass 6.0189 u ( He has Z = 2, that is 2 protons )

mass protons = 2 x 1.0078 u = 2.0516 u

mass neutrons = 4 x 1.0087 u = 4.0348 u

predicted mass = (2.0516 + 4.0348) u = 6.0504 u

mass defect = (6.0504 - 6.0189) u = 0.0315 u

Now we need to convert this mass expressed in atomic mass units to kilograms ( 1 u = 1.66054 x 10⁻²⁷ Kg )

0.0315 u x 1.66054 x 10⁻²⁷ Kg =5.231 x 10⁻²⁹ Kg

E =5.231x 10⁻²⁸ Kg x (3 x 10⁸ m/s )² = 4.707 x 10⁻¹²J

Finally we will convert this energy in Joules to eV

E = 4.707 x 10⁻¹² J x 6.242 x 10¹⁸ eV/J = 2.94 x 10⁷ eV = 29.4 MeV

E per nucleon for 6He = 29.4 MeV / 6 =4.90 MeV / Nucleon

Now the calculations for the rest of the nuclei are performed in similar manner with the following results:

8Li = 5.18 MeV / Nucleon

62Ni = 8.82 MeV / Nucleon

115 In = 8.54 MeV / Nucleon

8 0

3 years ago

Classify each of these reactions. A single reaction may fit more than one classification. Ba ( ClO 3 ) 2 ⟶ BaCl 2 + 3 O 2 Ba(ClO

Lena [83]

Answer: a) $Ba(ClO_3)_2\rightarrow BaCl_2+3O_2$ : Decomposition

b) $NaNO_2+HCl\rightarrow NaCl+HNO_2$ : double displacement

c) $CaO+CO_2\rightarrow CaCO_3$ : Synthesis (Combination)

d) $ZnSO_4+Mg\rightarrow MgSO_4+Zn$ : redox

Explanation:

Decomposition is a type of chemical reaction in which one reactant gives two or more than two products.

$Ba(ClO_3)_2\rightarrow BaCl_2+3O_2$

A double displacement reaction is one in which exchange of ions take place.

$NaNO_2+HCl\rightarrow NaCl+HNO_2$

Synthesis reaction is a chemical reaction in which two reactants are combining to form one product.

$CaO+CO_2\rightarrow CaCO_3$

Redox reaction is a type of chemical reaction in which oxidation and reduction takes place in one single reaction. The oxidation number of one element increases and the oxidation number of other element decreases.

$ZnSO_4+Mg\rightarrow MgSO_4+Zn$

4 0

3 years ago

The unit used to measure the diameter of an atom is an?

ohaa [14]

Answer:

Atomic Radii

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6 0

3 years ago

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