Thermochemistry lesson 2 - Hess cycles and enthalpy changes

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

Standard conditions are;

• 273 K 1 atm

• 20 ^oC 1 atm

• 25 ^oC 2 atm

• 298 K 1 atm

Tags

NGSS.HS-PS3-4

How can you convert Kelvin to Celcius?

• add 273
• subtract 273
• multiply by 273
• divide by 273

The amount of energy released or absorbed when one mole of a compound is formed from its elements

• heat of reaction
• heat of combustion
•  heat of completion
• heat of formation

Tags

NGSS.HS-PS1-4

Calculate ΔH° for the following reaction. The standard enthalpies of formation for the two reactants and two products are, in order, -1118, -110.5, -272, -393.5 (all in kJ/mol)

Fe₃O₄(s) + CO(g) →3FeO(s) + CO₂(g)

• -263 kJ

• 54 kJ

• 19 kJ

• -50 kJ

The enthalpy change for the reaction to form hydrated sodium thiosulfate crystals cannot be measured directly. The following Hess cycle can be used. The enthalpy change for the reaction, ΔHr, is equal to ...

• ΔH₁ + ΔH₂

• ΔH₁ − ΔH₂

• − ΔH₁ − ΔH₂

• − ΔH₁ + ΔH₂

The enthalpy change associated with a reaction carried out in multiple steps is ________ the sum of the enthalpy changes for each individual step.

• Greater than

• Equal to

• Less than

If you flip the equation, ΔH……

• Stays the same

• Is divided by 2

• Is multiplied by 2

• Flips too

What is a tool that measures the heat of chemical reactions?

• calorimeter
•  calorie
• Styrofoam™ cup
• none of these

Tags

NGSS.HS-PS1-4

which of the following enthalpy changes represent the enthalpy change of formation?

• Mg(s) + Cl₂(g) → MgCl₂(s)

• Mg²⁺(g) + 2 Cl ^-(g) → MgCl₂(aq)

• O2(g) → 2 O(g)

• 2Mg (s) + O₂(g) → 2MgO(S)

Tags

NGSS.HS-PS1-4