Chemical Energetics

The enthalpy change for the reaction, ∆H_r , is equal to

• ∆H₁ + ∆H₂

• ∆H₁ - ∆H₂

• -∆H₁ - ∆H₂

• -∆H₁ + ∆H₂

Tags

NGSS.HS-PS1-4

NGSS.HS-PS3-1

Given the following data: ΔH^○_f[FeO(s)] = –270kJmol^–1
ΔH^○_f [Fe₂O₃(s)] = –820 kJ mol^–1
Select the expression which gives the enthalpy change, in kJ mol^–1, for the reaction:
2FeO(s) + 1⁄2O₂(g) → Fe₂O₃(s) 

• (–820 × 1⁄2) + 270 = –140
• (+820 × 1⁄2) – 270 = +140
• –820 + (270 × 2) = –280 
• +820 – (270 × 2) = +280 

Tags

NGSS.HS-PS1-4

Use the chart to answer the following question.
Which is correct about energy changes during bond breaking and bond formation? 

• A
• B
• C
• D

Tags

NGSS.HS-PS1-4

C₂H₄(g) + H₂(g)   ->   C₂H₆(g)  ∆H°=-137 kJ mol^-1
Which statement about this information is correct?

• The total energy of the bonds broken in the reactants is greater 
  than the total energy of the bonds 
  formed in the product 
• The bonds broken and the bonds made are of the same strength 
• The total energy of the bonds broken in the reactants is less than the total energy of the bonds formed in the product 
• No conclusion can be made about the sums of the bond enthalpies in the product compared with the reactants 

Tags

NGSS.HS-PS1-4

Is the combustion of gasoline endothermic or exothermic?

• Endothermic
• Exothermic

Tags

NGSS.HS-PS1-4

ΔH value in an endothermic reaction is a positive number.

• True
• False

The enthalpies of combustion of C(s), H2(g) and C4H9OH(l) (in kJmol^-1) are as follows  
C(s) + O₂(g)   ->  CO₂(g)                                               ∆H=a
H₂(g) + ½O₂(g)   ->   H₂O(l)                                        ∆H=b
C₄H₉OH(l) + 6O₂(g)   ->   4CO₂(g) + 5H₂O(l)  ∆H=c
What is the enthalpy change for the reaction shown below?
  4C(g) + 5H₂(l) + ½O₂(g)   ->   C₄H₉OH(l)

• c – 4a – 5b
• 2a + 10b - c
• 4a + 5b - c
• 2a + 5b + c

Tags

NGSS.HS-PS1-4

Heat of Reaction

• The heat released after burning 1 mole of a substance.

• The amount of heat needed to melt 1 mole of a solid.

• The heat released by 1 mole of a substance as it changes from a liquid to a solid.

• The heat released or absorbed during a chemical reaction.

Tags

NGSS.HS-PS1-4

Enthalpy (H)

• The heat content of a system at constant pressure.

• A chemical equation that includes the amount of heat released or absorbed during the reaction.

• The heat released or absorbed during a chemical reaction.

• The heat released after burning 1 mole of a substance.

Tags

NGSS.HS-PS1-4

Endothermic reactions feel

• warm

• cold

Tags

NGSS.HS-PS1-4