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IrinaVladis [17]
3 years ago
15

We can also use the equation for enthalpy change for physical phase changes. Consider the phase change H2O(l) → H2O(g). Calculat

e ΔHrxn.
Use ΔHf values from the table above.

ΔHrxn = _____
Chemistry
2 answers:
DIA [1.3K]3 years ago
7 0
Standard molar enthalpy:
H2O ( liquid water ) : - 285.8 KJ/mole
H2O ( water vapor ) : - 241.8 KJ / mole.
ΔHrxn = - 241. 8 - ( - 285.8 )= -241.8 + 285.8 = 44.0
Answer: B ) 44.0 KJ  
VLD [36.1K]3 years ago
6 0

Answer: The value of enthalpy of the given reaction is 44.000 kJ/mol , that is energy is supplied to water to change into water vapors

Explanation:

H_2O(l)\rightarrow H_2O(g),\Delta H_{rxn}=?

Enthalpy of formation of water in liquid state,\Delta H_{f,H_2O(l)}=-285.820 kJ/mol

Enthalpy of formation of water in gaseous state,\Delta H_{f,H_2O(g)}=-241.820 kJ/mol

\Delta H_{rxn}=\sum \Delta H_f \text{of products}-\sum \Delta H_f \text{of reactants}

\Delta H_{rxn}=(-241.820 kJ/mol)-(-285.820 kJ/mol)=44.000 kJ/mol

The value of enthalpy of the given reaction is 44.000 kJ/mol, that is energy is supplied to water to change into water vapors.

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How much heat, in joules, is required to warm a metal disc from 19 °C to 33 °C? The
zalisa [80]

Answer:

Q = 96.6 j

Explanation:

Given data:

Heat required = ?

Initial temperature = 19°C

Final temperature = 33°C

Mass of disc = 3.0 g

Specific heat capacity = 2.3 J/g.°C

Solution:

Specific heat capacity:

It is the amount of heat required to raise the temperature of one gram of substance by one degree.

Formula:

Q = m.c. ΔT

Q = amount of heat absorbed or released

m = mass of given substance

c = specific heat capacity of substance

ΔT = change in temperature

ΔT = 33°C - 19°C

ΔT = 14°C

Q = 3.0 g×2.3 J/g.°C × 14°C

Q = 96.6 j

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2 years ago
Which of the following processes are exothermic?Which of the following processes are exothermic?Br(g) + e- → Br-(g)Li(s) → Li(g)
Ksenya-84 [330]

Answer:

The correct answer is:  None of the above are exothermic.

Explanation:

Energy is the ability to perform a job or to produce heat. Chemical reactions involve a rearrangement of atoms between substances with rupture or formation of chemical bonds and this generates changes in the energy of the system.

An exothermic reaction is that reaction where heat is released. This means that the energy of the molecules of the products is less than the energy of the molecules of the reactants.

An endothermic reaction is that chemical reaction that, when it occurs, consumes energy, that is, the products obtained have greater energy than the initial reagents, since they have taken part of the heat of the environment.

Sublimation is the change of state of a substance from solid to gas directly without going through the liquid state. This process requires energy to be carried out because the strong attractive energies between the solid molecules must be broken. So it is an endothermic process. This is what happens in the following reactions:

Li(s) → Li(g)

NaF(s) → Na+(g) + F-(g)

Dissociation is a process in which complexes, molecules or salts are separated into smaller molecules, ions or radicals, usually reversibly. Within the dissociation is the homolytic rupture, where each atom separates and carries the same charge of electrons. Thus free radicals are formed. To dissociate or break these bonds requires energy, so it is endothermic. This type of reaction occurs in:

Cl2(g) → 2Cl(g)

Electronic affinity is defined as the energy exchanged when an isolated and fundamental state gaseous atom takes an electron to form an anion (negative ion).  When the electronic affinity is greater than zero, the process would be endothermic and when the electroaffinity is less than zero, the process would be exothermic.

This occurs in:

Br(g) + e- → Br-(g)

The highest electronic affinities are for the elements of group 17 of the periodic table, the group to which bromine belongs. This means that the electronic affinity is greater than zero and is endothermic.

<u><em>The correct answer is:  None of the above are exothermic.</em></u>

<u><em>Br(g) + e- → Br-(g) </em></u>

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Answer:

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