Ch 13: Solids and Liquids

Ch 13 begins with notes from Ch 3.6 and 3.7 on Energy, Temperature and Heat.

We did not do these sections when in Ch 3 as the material is better discussed at the start of Ch 13.

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Ch 3.6 -- Energy, Temperature and Heat

• Energy is the capacity to do work– chemical, mechanical, thermal,

electrical, radiant, sound, nuclear

• Energy may affect matter– e.g. raising or lowering its

temperature will eventually cause a state change

ex: solid liquid gas

– All physical changes and chemical changes involve energy changes

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• Heat: a flow of energy due to a temperature difference

• Heat flows from a region of higher temp to a region of lower temp until equilibrium is reached. (see fig 3.12, 3.13, 3.14 on page 67)

Exothermic = A process that results in the evolution of heat.

•Example: when a match is struck, it releases energy as heat and light.

Endothermic = A process that absorbs energy.

•Example: melting ice absorbs heat from the environment to form liquid water.

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Ch 3.7 – Calculating Energy Changes

• Calculate the quantity of energy required for various processes.

• Units:– calorie (cal) -- is the amount of energy

needed to raise the temperature of one gram of water by 1°C A kilocalorie (kcal) = 1000 cal =

energy needed to raise the temperature of 1000 g of water by 1°C

In nutrition, a Calorie (capital C) is equal to one kcal (1000 cal)

– joule (J) – the SI unit of energy 4.184 J = 1 cal Converting J to cal (see example)

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Energy and the Temperature of Matter

• The temperature increase of an object depends on the amount of heat added (Q).– If the added heat energy is doubled, the

temperature of the object will double.

• The temperature increase of an object also depends on its mass– If the mass of the substance is doubled, it

will take twice as much heat energy to raise the temperature the same amount.

• Specific Heat Capacity (s) = the amount of energy required to raise the temperature of one gram of a substance by one degree Celsius. Units of s = J/g oC

Q = s X m X ∆T

Q = energy (heat) required s = specific heat capacity of substancem = mass of substance in grams∆T = change in temperature in oC

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Example 1: Converting calories to joules:

Example 2:Calculate the amount of heat energy (in joules) needed to raise the temperature of 7.40 g of water from 29.0°C to 46.0°C

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Example 3:A 1.6 g sample of metal that appears to be gold requires 5.8 J to raise the temperature from 23°C to 41°C.

Is the metal pure gold?

C gJ