7.6 Hess's Law

Using the equations below:

C(s) + O₂(g) → CO₂(g) ∆H = –390 kJ

Mn(s) + O₂(g) → MnO₂(s) ∆H = –520 kJ

what is ∆H (in kJ) for the following reaction?

MnO₂(s) + C(s) → Mn_(s) + CO₂(g)

• 910

• 130

• -130

• -910

Tags

NGSS.HS-PS1-4

NGSS.HS-PS3-1

NGSS.HS-PS1-2

Using the equations below

Cu(s) + ¹/₂O₂(g) → CuO(s) ∆H = –156 kJ

2Cu(s) + O₂(g) → Cu₂O(s) ∆H = –170 kJ

what is the value of ∆H (in kJ) for the following reaction?

2CuO(s) → Cu₂O(s) + ¹/₂O₂(g)

• 142

• 15

• -15

• -142

Tags

NGSS.HS-PS1-4

NGSS.HS-PS3-1

Consider the following equations.

Mg(s) + O₂(g) → MgO(s) ∆H = –602 kJ

H₂(g) + O₂(g) → H₂O(g) ∆H = –242 kJ

What is the ∆H value (in kJ) for the following reaction?

MgO(s) + H₂(g₎ → Mg(s) + H₂O(g)

• -844

• -360

• +360

• +844

Tags

NGSS.HS-PS1-4

The following equations show the oxidation of carbon and carbon monoxide to carbon dioxide.

C(s) +O₂(g) → CO₂(g) ΔH = –x kJ mol^–1

CO(g) + O₂(g) → CO₂(g) ΔH = –y kJ mol^–1

What is the enthalpy change, in kJ mol^–1, for the oxidation of carbon to carbon monoxide?

C(s) + O₂(g) → CO(g)

• x + y

• -x - y

• y - x

• x - y

Tags

NGSS.HS-PS1-4

In an endothermic reaction the system is releasing energy.

• True
• False
• Sometimes

In an exothermic reaction, heat is ...

• taken in
• given out
• nothing happens
• it gets colder

Tags

NGSS.HS-PS1-4

A chemical reaction that requires energy is a(n)

• exothermic reaction 
• endothermic reaction 
• over reaction 
• redox reaction

Tags

NGSS.HS-PS1-4

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

• 86 kJ

• - 86 kJ

• 68 kJ

• -68 kJ

How much energy is required to turn 1 mole of N₂O₄(g) into 2 moles N & 4 moles O(g)?

• 1933 kJ

• -1875 kJ

• - 1933 kJ

• 1875 kJ

Tags

NGSS.HS-PS1-4

NGSS.HS-PS3-1