Thermodynamics Assessment Study Guide

Question 1

What does the Law of Conservation of Energy state?

Answer 1

Energy cannot be created or destroyed, but can be transferred between the system and surroundings and change forms.

Question 2

What is energy? List three different types of energy.

Answer 2

Energy is the ability to do work, or the transfer of heat. It is typically measured in Joules (J). Examples: Thermal, Chemical, Potential, Kinetic, Nuclear, Electrical

Question 3

What are the differences between exothermic and endothermic processes/reactions?

Answer 3

Exothermic processes/reactions release heat from the system to the surroundings. The container will feel warm.
Endothermic processes/reactions absorb heat from the surroundings into the system. The container will feel cool.

Question 4

What is the difference between heat and temperature?

Answer 4

Heat measures how energy moves from one place to another, or between system and surroundings.
Temperature is the measure of the kinetic energy of the molecules within a system.
Heat and temperature are related, but are not the same thing!

Question 5

You should know how to utilize the equation q = mcΔT, and should be able to solve for all of the variables.

Answer 5

q = heat (Joules, J) c = specific heat capacity (J/g ˚C)
m = mass (grams, g) ΔT = change in temperature = Tfinal - Tinitial (˚C)

Question 6

What is the specific heat of a substance if it needs 3,025 J to change a 53 g substance from 15 ˚C to 35 ˚C?

Answer 6

3025 = 53c(35-15) c=30251060
3025 = 1060*c c = 2.85 J/ g˚C

Question 7

What is the mass of aluminum if it takes 1,000 J to raise the temperature from 10 ˚C to 28 ˚C? The specific heat of aluminum is 0.899 J/g ˚C.

Answer 7

q = 1000, ΔT = 18, c = 0.899
1000 = m (0.899)(18)
m = 61.8 grams

Question 8

The combustion of 1.2 moles of methane (CH4) produced a temperature increase of 11.0 °C in 850 g of water. The specific heat of water is c = 4.184 J/g ˚C.
What is the heat (q) released by this reaction?

Calculate the enthalpy change (∆H)

Is this endothermic or exothermic?

Answer 8

q = mcΔT = 850 g * 4.184 J/g ˚C. * 11 C = 39120.4 joules

q (methane) = - q (water)
∆H = q/moles = -39,120.4 joules /1.2 moles = -32,600 joules/mole

exothermic - it releases energy

Question 9

Label the following thermochemical equations as either exothermic or endothermic:
CO2 + H2O + heat → C6H12O6 + O2

Answer 9

Endothermic. Heat is on the reactant side, meaning that heat must be absorbed for the reaction to take place.

Question 10

Label the following thermochemical equations as either exothermic or endothermic:
4 Fe + 3 O2 → 2 Fe2O3 + heat

Answer 10

Exothermic. Heat is on the product side, meaning that heat must be released for the reaction to take place.

Question 11

Label the following as either endothermic or exothermic:
Water freezing to become ice.

Answer 11

Exothermic. Heat must be released in order for water to freeze and turn from a liquid to a solid.

Question 12

Label the following as either endothermic or exothermic
An ice pack being activated.

Answer 12

Endothermic. When the surroundings get cold, that means heat is being absorbed by the system, making it endothermic.

Question 13

Label the following as either endothermic or exothermic
Mixing calcium chloride and water in a test tube, and the test tube getting warm.

Answer 13

Exothermic. When the surroundings get warm, that means heat is being released by the system, making it exothermic.

Question 14

Calculate the enthalpy change (∆H) for the dissolution of 2.5 moles of hydrochloric acid that releases 10,540 J of heat.

Answer 14

delta H=qmoles
delta H=105402.5= 4,216 J/mole