Entropy, Enthalpy, and Gibbs' Energy

Which one of these would result in a decrease in entropy?

• A solid solute dissolves in water.
• A gas is released.
• A liquid freezes.
• A liquid boils.

Entropy always increases when

• enthalpy decreases.
• temperature decreases.
• temperature increases.
• volume increases.

Tags

NGSS.HS-PS3-4

Hess' Law states...

• the change of enthalpy in a chemical reaction is dependent of the pathway between the initial and final states

• the change of enthalpy in a chemical reaction is independent of the pathway between the initial and final states

Entropy is...

• the natural progression from order to disorder

• the natural progression from disorder to order

The change in enthalpy (delta H) is...

• the difference between the energy used to break bonds in a chemical reaction and the energy gained by the formation of new chemical bonds in the reaction

• made up by scientists to confuse you

• the difference between the energy used to break bonds in a chemical reaction

• the difference between the energy gained by the formation of new chemical bonds in the reaction

The standard enthalpy changes of combustion of carbon, hydrogen and methane are shown in the table. 
Which one of the following expressions gives the correct value for the standard enthalpy change of formation of methane in kJ mol^–1?
C(s) + 2H₂(g) → CH₄(g) 

• 394 + (2 × 286) – 891 
• –394 – (2 × 286) + 891 
• 394 + 286 – 891 
• –394 – 286 + 891 

Tags

NGSS.HS-PS1-4

(Hess's Law)Calculate the ∆H for the following reaction: 2H₂O₂ →  2H₂O  + 1 O₂ 
You are given these two equations:
2H₂  +  O₂ → 2H₂O            ∆H  =  -572 kJ
H₂  +  O₂  →  H₂O₂            ∆H  =  -188 kJ 

• ∆H  =  -948 kJ 
• ∆H  =  -196 kJ 
• ∆H  =  -384 kJ 
• ∆H  =  -188 kJ 

Tags

NGSS.HS-PS1-4

NGSS.HS-PS3-1

Which reaction has the greatest decrease in entropy?

• 2H₂ (g) +O₂(g) => 2H₂O(l)

• H₂O(g) => H₂O(l)

• 2H₂ (g) +O₂(g) => 2H₂O(g)

• H₂O(g) => H₂O(s)

When liquid condenses, what are the signs for Δ H and Δ S ?

• Δ H = + Δ S = +

• Δ H = - Δ S = -

• Δ H = + Δ S = -

• Δ H = - Δ S = +

Calculate ΔH° for the combustion of methane.

CH₄ (g) + 2 O₂ (g) → CO₂ (g) + 2 H₂O (g)

Given the enthalpies of formation below.

CH₄ (g): -50.8 kJ/mol

O₂ (g): 0 kJ/mol

CO₂ (g): -394.4 kJ/mol

H₂O (g): -228.57 kJ/mol

• -801kJ/mol

• +801kJ/mol

• +572kJ/mol

• -572kJ/mol