Specific Heat Essay

Study Guide: Thermodynamics test
▪ What is specific heat?
▪ Be able to use the formulat E = sm
Δ
T to calculate the energy absorbed/released by a substance as it cools down. A chemical reaction is carried out in a calorimeter. The temperature of the solution
(water) increases from 21 to 27.5 deg C. If the mass of the solution is 100 g, and its specific heat is 4.18 J/g deg C, what is the energy released by the reaction in Joules? ▪ Be able to calculate specific heat (c), given the change in temp, mass, and energy absorbed/released, and mass of an object, given the change in temp, specific heat and energy absorbed/released…. 100 g of water at 22.4 deg C is placed in a calorimeter. A 74.24 g sample of aluminum is removed from boiling water at a temperature of 99.3 deg C and quickly placed in the calorimeter with the water. The substances reach a final temperature of
32.9 deg C.
What is the specific heat of aluminum? ● Know the difference between a coffee cup calorimeter and a bomb calorimeter. What is the heat capacity of a bomb calorimeter, and how is it used to calculate the enthalpy of a reaction using a bomb calorimeter. ● Be able to define boiling and explain (using that definition) how a change in atmorspheric pressure affects boiling point (i.e. altitude, pressure cooker, etc) ▪ Be able to follow a phase diagram and calculate the amount of energy it takes… How much energy would be required to convert 15 g of water at 22 deg C to steam at 102 deg C? (specific heat of water = 4.18 J/g deg C, specific heat of steam = 1.99 J/g deg C, heat of vaporatizion = 2260 J/g Which will be more likely to burn you – 15 g of water at 100 deg C? or 15 g of steam at
100 deg C? Why?? ▪ What is the heat of a reaction? What sign doe
Δ
H have if a reaction is endothermic? exothermic? ▪ Be able to draw an energy diagram for both exothermic and endothermic reactions
▪ Be able to write the chemical equations the show the heats of formation for any chemical substance (remember what the heat of formation for elements in their standard states always is…)
▪ Be able to determine the
Δ
H for a reaction using the heats of formation
▪ Understand how to use Hess’s Law to obtain the DH for a reaction comprised of several steps. Calculate
Δ
H for the reaction NO(g) + O(g) → NO
(g)
2
NO(g) + O
(g) → NO
(g) + O
(g)
Δ H = 198.9 kJ 3
2
2
O
(g) → 3/2 O
(g)
Δ H = 142.3 kJ 3
2
O
(g) → O(g)
Δ

H = 495 kJ 2 Calculate
Δ
H for the reaction P
O
(s) + 2O
(g) → P
O
4
6
2
4
10
P
(s) + 3O
(g) → P
O
(s)
DH = 1640.1 kJ
4
2
4 6
P
(s) + 5 O
(g) → P O
(s)
DH = 2940.1 kJ
4
2
4
10 ▪ What is entropy? What does it measure?

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▪
▪
▪
▪
▪

As a system becomes more disordered, does
Δ
S increase or decrease? Which value for
Δ
S (+ or ) will drive a reaction to become more spontaneous?
Be able to recognize if a reaction is increasing or decreasing in entropy
What is free energy? What does it measure
Δ
G =
Δ
H =T

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