Thermochemistry

THERMODYNAMICS

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Ch 17 textbook

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Thermochemistry

First Law of Thermodynamics

• Energy is neither created nor destroyed.

• In other words, the total energy of the universe is a constant; if the system loses energy, it must be gained by the surroundings, and vice versa.

Thermochemistry

Changes in Internal Energy

• When energy is exchanged between the system and the surroundings, it is exchanged as either heat (q) or work (w).

• That is, E = q + w.

Thermochemistry

Calorimetry The amount of heat absorbed or released during a

physical or chemical change can be measured,

usually by the change in temperature of a known

quantity of water in a calorimeter.

Thermochemistry

Heat Capacity and Specific Heat

• The amount of energy required to raise the temperature of a substance by 1 K (1C) is its heat capacity.

• We define specific heat capacity (or simply specific heat) as the amount of energy required to raise the temperature of 1 g of a substance by 1 K.

Thermochemistry

Specific Heat

Substance Specific Heat (J/g·K)

Water (liquid) 4.18

Ethanol (liquid) 2.44

Water (solid) 2.06

Water (vapor) 1.87

Aluminum (solid) 0.897

Carbon (graphite,solid) 0.709

Iron (solid) 0.449

Copper (solid) 0.385

Mercury (liquid) 0.140

Lead (solid) 0.129

Gold (solid) 0.129

The amount of heat required to raise the temperature of

one gram of substance by one degree Celsius.

Thermochemistry

Calculations Involving Specific Heat

c = Specific Heat Capacity

q = Heat lost or gained

T = Temperature change

𝑞 = 𝑐 × 𝑚 × ∆𝑇

m = mass

Thermochemistry

Calculate the amount of heat lost or gained by a

3.46 g sample of aluminum when the

temperature raises from 25.0°C to 45°C.

(Specific heat of aluminum = 0.902 J/g•°C) Is

this endothermic or exothermic? Why?

Thermochemistry

Calculate the amount of heat lost or gained by a

3.46 g sample of aluminum when the

temperature raises from 25.0°C to 45°C.

(Specific heat of aluminum = 0.902 J/g•°C) Is

this endothermic or exothermic? Why?

Thermochemistry

Determine the heat transferred from a piece of

metal heated to 85.0C when it is placed in a

coffee cup calorimeter with 150.0 g of water

initially at 22.5C and equilibrates with the water

at 32.1C.

If the piece of metal had a mass of 157.52g, then

what was the specific heat of the metal?

Thermochemistry

Determine the heat transferred from a piece of

metal heated to 85.0C when it is placed in a

coffee cup calorimeter with 150.0 g of water

initially at 22.5C and equilibrates with the water

at 32.1C.

If the piece of metal had a mass of 157.52g, then

what was the specific heat of the metal?

Thermochemistry

A 28.4 g sample of aluminum is heated

to 39.4 oC, then is placed in a

calorimeter containing 50.0 g of water.

Temperature of water increases from

21.00 oC to 23.00 oC. What is the

specific heat of aluminum?

Thermochemistry

A 28.4 g sample of aluminum is heated

to 39.4 oC, then is placed in a

calorimeter containing 50.0 g of water.

Temperature of water increases from

21.00 oC to 23.00 oC. What is the

specific heat of aluminum?