T-2: Enthalpy Flashcards Preview

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Flashcards in T-2: Enthalpy Deck (27):
1

Energy required to break a chemical bond

Bond Energy

2

Standard states

Phase at 25ºC,  1 atm for gases and 1 M for solutions.

3

Energy change that occurs when you make one mole of a compound from its constituent elements at standard states

Standard Enthalpy of Formation

4

The equation to find ΔHº from standard enthalpies of formation

ΔHº = Σ(nΔHºf,prod) - Σ(nΔHºf, react)

5

The equation to find ΔH from bond energies.

ΔH = Σ(nB.E.broken) - Σ(nB.E.formed)

6

The amount of energy required to break a chemical bond.

Bond energy

7

Bond Energy

Energy required to break a chemical bond

8

Phase at 25ºC,  1 atm for gases and 1 M for solutions.

Standard states

9

Standard Enthalpy of Formation

Energy change that occurs when you make one mole of a compound from its constituent elements at standard states

10

ΔHº = Σ(nΔHºf,prod) - Σ(nΔHºf, react)

The equation to find ΔHº from standard enthalpies of formation

11

ΔH = Σ(nB.E.broken) - Σ(nB.E.formed)

The equation to find ΔH from bond energies.

12

Bond energy

The amount of energy required to break a chemical bond.

13

Exothermic or Endothermic

Breaking a covalent bond

Endothermic

14

Exothermic or Endothermic

Making a covalent bond

exothermic

15

Exothermic or Endothermic

F2(g) → 2F(g)

endothermic - breaking a bond

16

Exothermic or Endothermic

2Br(g) → Br2(g)

exothermic - making a bond

17

Exothermic or Endothermic

Li+(g) + Cl-(g) → LiCl(s)

exothermic - making a bond

18

Exothermic or Endothermic

NaF(s) → Na+(g) + F-(g)

endothermic - breaking a bond

19

Write out reaction equation for standard enthalpy of formation for HCl.

1/2H2(g) + 1/2Cl2(g) → HCl(g)

20

Write out reaction equation for standard enthalpy of formation for CO2.

C(s) + O2(g) → CO2(g)

21

S8(s) + 8 O2(g) →8 SO2 (g)

Write this reaction as a enthalpy of formation for SO2

1/8 S8(s) + O2(g) → SO2(g)

22

The ΔHº for the following reaction is...

1/2H2(g) + 1/2Cl2(g) → HCl(g)        ΔHº = -92 kJ/mol

What is the ΔHº for this reaction?

H2(g) + Cl2(g) → 2 HCl(g) 

 ΔHº = - 184 kJ/mol 

- multiply reaction by 2 so multiple value by 2

23

The ΔHº for the following reaction is...

1/2H2(g) + 1/2Cl2(g) → HCl(g)        ΔHº = -92 kJ/mol

What is the ΔHº for this reaction?

HCl(g) → 1/2H2(g) + 1/2Cl2(g) 

 ΔHº = 92 kJ/mol 

- reverse reaction so reverse sign

24

The ΔHº for the following reaction is...

1/2H2(g) + 1/2Cl2(g) → HCl(g)        ΔHº = -92 kJ/mol

What is the ΔHº for this reaction?

2 HCl(g) → H2(g) + Cl2(g) 

 ΔHº = 184 kJ/mol 

- reversed the reaction so reverse the sign

- multiplied reaction by 2 so multiple value by 2

25

The bond energy for O2 (O=O) is 498 kJ/mol.  What does that mean?

It takes 498 kJ of energy to break 1 mole of O2 molecules into individual oxygen atoms.

26

The bond energy for C-H is 439 kJ/mol.  How much energy is released when 4 moles of hydrogen atoms bind to 1 mole of carbon atoms?

(439)4 = 1756 kJ are liberated for each mole of CH4 produced in this way.

27

It takes 872 kJ to break apart 2 moles of H2 molecules to form 4 moles of H atoms.  1756 kJ of energy are liberated when 4 moles of hydrogen atoms bind to 1 mole of carbon atoms.  How much energy is liberated/absorbed when 2 mole of H2 molucules combine with 1 mole of C atoms?

ΔH = sum of bonds broken - sum of bonds formed so ΔH = 872 kJ - 1756 kJ = - 884 kJ - Exothermic