Units

Calculations

Energy

Vocab

Temperature

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What is the SI unit for temperature?

Kelvin

What is the unit for molar heat capacity?

J/K∙mol

What is the unit for n?

mol

What is the unit of energy? Write the word and symbol on the board.

Joules, J

What is the unit for molar enthalpy?

J/mol

What is the generic equation for changing Celsius into Kelvin.

° C + 273= K

Use this equation if you are finding the change in heat for 25g of water.

q =nC∆T

Use this equation if you are finding the molar enthalpy change and do not have the amount in moles.

∆ H=C∆T

What is the generic equation for finding the change in enthalpy for a reaction using Enthalpies of Formation?

∆H= ∆H° f products- ∆H° f reactants

Calculate the change in enthalpy when forming aluminum oxide. 2Al(s) + 3H 2 O(l)→ Al 2 O 3 (s) + 3H 2 (g) ∆H f H2O = kJ/mol ∆H f Al2O3 = kJ/mol

(3x-285.8)= kJ/mol

If the energy change in a reaction is negative the reaction is __________.

Exothermic

When ∆H is positive, the reaction is __________.

Endothermic

What is the only way we measure energy?

With a thermometer

Calculate the molar enthalpy change of N 2 (g) when it is heated from 90.0°C to 100.°C. The molar heat capacity of nitrogen is 29.1 J/K∙mol. Don’t forget to round to the correct sig figs.

291 J/mol

Calculate ∆H for this reaction: 3Fe 2 O 3 (s) → 6Fe(s) + 4.5O 2 (s) 3Fe 2 O 3 (s)→2Fe 3 O 4 (s) + 1/2O 2 (s) ∆H=-316kJ/mol 3Fe(s) + 2O 2 (g) → Fe 3 O 4 (s) ∆H=-201kJ/mol.

86kJ/mol

Define molar heat capacity. Hint: think about the units

The amount of energy required to raise 1 mole of a substance 1K.

Define extensive property.

A property that depends on the amount of substance, like heat.

Define intensive property. Is heat or temperature intensive?

A property that is independent of the amount of substance, like temperature.

Define heat.

The energy transferred between two objects of different temperatures.

Define Hess’s Law.

The change in enthalpy for a reaction is equal to the sum of the individual enthalpy changes.

Define temperature.

The average kinetic energy of the particles in an object.

Convert 17°C to Kelvin.

17°C + 273= 315K

Correctly write the standard thermodynamic temperature in Celsius and Kelvin on the board. This is the temp that the reactants are at for all heat measurements

25°C and 298K (no degree symbol for K)

What is ∆T in Kelvin if an object is cooled from 50°C to 30°C.

20K

What is the generic equation when solving for ∆T in this equation: q=nC∆T?

∆T = q/nC

Write the symbol(s) for “the change in temperature” on the board.

∆T

How many sig figs does the following measurements have? a. 4500J b. 350.J c J

a. 4500J= 2 b. 350.J = 3 c J = 4

What do all the variables in q=nC∆T represent?

q= heat n= moles C= molar heat capacity ∆T = temperature

This chapter is about Thermodynamics, it is the study of _______ changes.

energy

Explain why a balloon with 50mL of water in it won’t pop when a flame is held to it.

Because the molar heat capacity of water is high (which means it takes a lot of energy to heat water). and the energy from the flame is transferred to the water before the balloon.

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