The standard heat of combustion of a hydrocarbon compound is ana

EASY

Physical Sciences>Matter and Its Interactions>Use mathematical representations to support the claim that atoms, and therefore mass, are conserved during a chemical reaction.>Chemical Reactions - The fact that atoms are conserved, together with knowledge of the chemical properties of the elements involved, can be used to describe and predict chemical reactions.

The enthalpy change on freezing of

1 mol

of water at

5 ° C

to ice at

- 5 ° C

is:

(Given

Δ_{fus} H = 6 kJ {mol}^{- 1}

at

0 ° C,

C_{p} (H_{2} O, l) = 75 .3 J {mol}^{- 1} K^{- 1}

C_{p} (H_{2} O, s) = 36 .8 J {mol}^{- 1} K^{- 1}

)

EASY

Physical Sciences>Matter and Its Interactions>Use mathematical representations to support the claim that atoms, and therefore mass, are conserved during a chemical reaction.>Chemical Reactions - The fact that atoms are conserved, together with knowledge of the chemical properties of the elements involved, can be used to describe and predict chemical reactions.

Consider the reaction,

N_{2} + 3 H_{2} \to 2 {NH}_{3}

, carried out at a constant temperature and pressure. If

ΔH

and

ΔU

are the enthalpy and internal energy changes for the reaction, which of the following expressions is true?

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Physical Sciences>Matter and Its Interactions>Use mathematical representations to support the claim that atoms, and therefore mass, are conserved during a chemical reaction.>Chemical Reactions - The fact that atoms are conserved, together with knowledge of the chemical properties of the elements involved, can be used to describe and predict chemical reactions.

The standard enthalpies of formation of ${CO}_{2} (g)$ $, H_{2} O (l)$ and glucose (s) at $2 5^{o} C$ are $- 400 kJ / mol$ , $- 300 kJ / mol$ and $- 1300 kJ / mol$ , respectively. The standard enthalpy combustion per gram of glucose at $2 5^{o} C$ is

( ${ΔH}_{f}^{0} = - 1300 kJ {mol}^{- 1}$ for Glucose)

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Physical Sciences>Matter and Its Interactions>Use mathematical representations to support the claim that atoms, and therefore mass, are conserved during a chemical reaction.>Chemical Reactions - The fact that atoms are conserved, together with knowledge of the chemical properties of the elements involved, can be used to describe and predict chemical reactions.

Given that the bond energies of:

N \equiv N is 946 kJ {mol}^{- 1}, H - H is 435 kJ {mol}^{- 1}, N - N is 159 kJ {mol}^{- 1},

and

N - H is 389 kJ {mol}^{- 1}

, the heat of formation of hydrazine in the gas phase in

kJ {mol}^{- 1}

is:

EASY

Physical Sciences>Matter and Its Interactions>Use mathematical representations to support the claim that atoms, and therefore mass, are conserved during a chemical reaction.>Chemical Reactions - The fact that atoms are conserved, together with knowledge of the chemical properties of the elements involved, can be used to describe and predict chemical reactions.

The heat of combustion of carbon to

C O_{2}

is

- 393.5 kJ / mol

. The heat released upon the formation of

35.2 g

of

C O_{2}

from carbon and oxygen gas is

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Physical Sciences>Matter and Its Interactions>Use mathematical representations to support the claim that atoms, and therefore mass, are conserved during a chemical reaction.>Chemical Reactions - The fact that atoms are conserved, together with knowledge of the chemical properties of the elements involved, can be used to describe and predict chemical reactions.

For the reaction

N_{2} + 3 X_{2} \to 2 {NX}_{3}

where

X = F, Cl

(the average bond energies are

F - F = 155 kJ {mol}^{- 1}, N - F = 272 kJ {mol}^{- 1}, Cl - Cl = 242 kJ {mol}^{- 1}, N - Cl = 200 kJ {mol}^{- 1}

and

N \equiv N = 941 kJ {mol}^{- 1}

), the heats of reaction of

{NF}_{3}

and

{NCl}_{3}

in

kJ {mol}^{- 1},

respectively, are closest to

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Physical Sciences>Matter and Its Interactions>Use mathematical representations to support the claim that atoms, and therefore mass, are conserved during a chemical reaction.>Chemical Reactions - The fact that atoms are conserved, together with knowledge of the chemical properties of the elements involved, can be used to describe and predict chemical reactions.

One mole of ethanol is produced reacting graphite,

H_{2}

and

O_{2}

together. The standard enthalpy of formation is

- 277.7 k J m o l^{- 1} .

Calculate the standard enthalpy of the reaction when

4

moles of graphite is involved

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Physical Sciences>Matter and Its Interactions>Use mathematical representations to support the claim that atoms, and therefore mass, are conserved during a chemical reaction.>Chemical Reactions - The fact that atoms are conserved, together with knowledge of the chemical properties of the elements involved, can be used to describe and predict chemical reactions.

The heats of combustion of carbon and carbon monoxide are

- 393.5 a n d - 283.5 k J m o l^{- 1},

respectively. The heat of formation

(in kJ)

of carbon monoxide per mole is:

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Physical Sciences>Matter and Its Interactions>Use mathematical representations to support the claim that atoms, and therefore mass, are conserved during a chemical reaction.>Chemical Reactions - The fact that atoms are conserved, together with knowledge of the chemical properties of the elements involved, can be used to describe and predict chemical reactions.

The heat of atomization of methane and ethane are

360 kJ {mol}^{- 1}

and

620 kJ {mol}^{- 1}

, respectively. The longest wavelength of light capable of breaking the

C - C

bond is (Avogadro's number

= 6.023 \times 10^{23}, h = 6.62 \times 10^{- 34} J s

)

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Physical Sciences>Matter and Its Interactions>Use mathematical representations to support the claim that atoms, and therefore mass, are conserved during a chemical reaction.>Chemical Reactions - The fact that atoms are conserved, together with knowledge of the chemical properties of the elements involved, can be used to describe and predict chemical reactions.

Given:

C (graphite) + O_{2} (g) \to {CO}_{2} (g); Δ_{r} H^{o} = - 393 .5 kJ {mol}^{- 1}

H_{2} (g) + \frac{1}{2} O_{2} (g) \to H_{2} O (l); Δ_{r} H^{o} = - 285 .8 kJ {mol}^{- 1}

{CO}_{2} (g) + 2 H_{2} O (l) \to {CH}_{4} (g) + 2 O_{2} (g); Δ_{r} H^{o} = + 890 .3 kJ {mol}^{- 1}

Based on the above thermochemical equations, the value of

Δ_{r} H^{o}

at

298 K

for the reaction

C (graphite) + 2 H_{2} (g) \to {CH}_{4} (g)

will be:

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Physical Sciences>Matter and Its Interactions>Use mathematical representations to support the claim that atoms, and therefore mass, are conserved during a chemical reaction.>Chemical Reactions - The fact that atoms are conserved, together with knowledge of the chemical properties of the elements involved, can be used to describe and predict chemical reactions.

For complete combustion of ethanol,

C_{2} H_{5} OH (l) + 3 O_{2} (g) \to 2 {CO}_{2} (g) + 3 H_{2} O (l)

,
the amount of heat produced as measured in bomb calorimeter, is

{1364.47 kJ mol}^{-1}

at

25 ℃

. Assuming ideality the Enthalpy of combustion,

Δ_{c} H

, for the reaction will be:

(R = {8.314 kJ mol}^{-1})

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Physical Sciences>Matter and Its Interactions>Use mathematical representations to support the claim that atoms, and therefore mass, are conserved during a chemical reaction.>Chemical Reactions - The fact that atoms are conserved, together with knowledge of the chemical properties of the elements involved, can be used to describe and predict chemical reactions.

Calculate the enthalpy change. For the change $8 S (g) \to S_{8} (g)$ , given that

$H_{2} S_{2} (g) \to 2 H (g) + 2 S (g), ΔH = 239 .0 k c a l m o l^{- 1}$

$H_{2} S (g) \to 2 H (g) + S (g), ΔH = 175 .0 k c a l m o l^{- 1}$

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Physical Sciences>Matter and Its Interactions>Use mathematical representations to support the claim that atoms, and therefore mass, are conserved during a chemical reaction.>Chemical Reactions - The fact that atoms are conserved, together with knowledge of the chemical properties of the elements involved, can be used to describe and predict chemical reactions.

The standard enthalpy of formation of

{NH}_{3}

is

- 46.0 kJ / mol

. If bond enthalpy of

H_{2}

is

- 436 kJ / mol

and that of

N_{2}

is

- 712 kJ / mol

, the average bond enthalpy of

N - H

bond in

{NH}_{3}

is :

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Physical Sciences>Matter and Its Interactions>Use mathematical representations to support the claim that atoms, and therefore mass, are conserved during a chemical reaction.>Chemical Reactions - The fact that atoms are conserved, together with knowledge of the chemical properties of the elements involved, can be used to describe and predict chemical reactions.

For a reaction,

A (g) \to A (l); ΔH = - 3 RT .

The correct statement for the reaction is

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Physical Sciences>Matter and Its Interactions>Use mathematical representations to support the claim that atoms, and therefore mass, are conserved during a chemical reaction.>Chemical Reactions - The fact that atoms are conserved, together with knowledge of the chemical properties of the elements involved, can be used to describe and predict chemical reactions.

The combustion of benzene

(l)

gives

{CO}_{2} (g)

and

H_{2} O (l) .

Given that heat of combustion of benzene at constant volume is

- 3263 .9 kJ {mol}^{- 1}

at

25 ° C;

the heat of combustion

(in kJ {mol}^{- 1})

of benzene at constant pressure will be

(R = 8 .314 {JK}^{- 1} {mol}^{- 1})

EASY

Physical Sciences>Matter and Its Interactions>Use mathematical representations to support the claim that atoms, and therefore mass, are conserved during a chemical reaction.>Chemical Reactions - The fact that atoms are conserved, together with knowledge of the chemical properties of the elements involved, can be used to describe and predict chemical reactions.

The difference between

∆ H

and

∆ U

is

(∆ H - ∆ U)

, when the combustion of one mole of heptane

(l)

is carried out at a temperature

T

, is equal to:

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Physical Sciences>Matter and Its Interactions>Use mathematical representations to support the claim that atoms, and therefore mass, are conserved during a chemical reaction.>Chemical Reactions - The fact that atoms are conserved, together with knowledge of the chemical properties of the elements involved, can be used to describe and predict chemical reactions.

For silver,

C_{p} (J K^{- 1} m o l^{- 1}) = 23 + 0.01 T .

If the temperature

(T)

of

3

moles of silver is raised from

300 K t o 1000 K a t 1 a t m

pressure, the value of

Δ H

will be close to:

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Physical Sciences>Matter and Its Interactions>Use mathematical representations to support the claim that atoms, and therefore mass, are conserved during a chemical reaction.>Chemical Reactions - The fact that atoms are conserved, together with knowledge of the chemical properties of the elements involved, can be used to describe and predict chemical reactions.

Identify the INVALID equation.

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Physical Sciences>Matter and Its Interactions>Use mathematical representations to support the claim that atoms, and therefore mass, are conserved during a chemical reaction.>Chemical Reactions - The fact that atoms are conserved, together with knowledge of the chemical properties of the elements involved, can be used to describe and predict chemical reactions.

The bond dissociation energies of

X_{2} Y_{2}

and

XY

are in the ratio of

1 : 0 .5 : 1 . ΔH

for the formation of

XY

is

- 200 kJ {mol}^{- 1}

. What will be the bond dissociation energy of

X_{2}

?

EASY

Physical Sciences>Matter and Its Interactions>Use mathematical representations to support the claim that atoms, and therefore mass, are conserved during a chemical reaction.>Chemical Reactions - The fact that atoms are conserved, together with knowledge of the chemical properties of the elements involved, can be used to describe and predict chemical reactions.

For which of the following reactions,

∆ H

is equal to

∆ U

?

The standard heat of combustion of a hydrocarbon compound is an/a-

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