The Measurement of Heat Calorimetry

Kinetic molecular theory Collective hypotheses about the particulate nature of matter and the surrounding space Greeks - earliest written ideas on atoms Current view –Matter comprised of microscopic particles - atoms –Atoms combine to form molecules –Many macroscopic phenomena can be traced to interactions on this level

What do we mean by “hot” and “cold”? Hot: Having a temperature that is higher than surrounding objects. Cold:Having a temperature that is lower than surrounding objects

The Common Temperature Scales Fahrenheit & Celsius Celsius & Kelvin

What is temperature? Temperature is the measurement we use to express the average kinetic energy of motion (vibration) of all the atoms and molecules in an object. This kinetic energy of motion of particles is called “thermal energy.” All objects have some average thermal energy. The greater/lower it is, the greater/lower is the temperature of the object.

1848 William Thomson a.k.a. Lord Kelvin 0 K supernova core 100,000,000,000 K core of sun 15,000,000 K surface of sun 6,000 K lava 1,200 K ice 273 K Room temperature 294 K dry ice 164 K liquid nitrogen 77 K liquid He 4 K dilution refrigerator K Universe 2.7 K triple point cell K absolute zero

Absolute Zero (0K)

What is Heat? Heat is thermal energy that is transferred from one object to another. An object will transfer thermal energy (as heat) to another object that is at a lower temperature UNTIL both objects reach the SAME TEMPERATURE (thermal equilibrium). On its own, heat only moves from hotter objects to cooler objects.

HOTCOLD same Time passes Object B Object A

Heat versus temperature Temperature A measure of hotness or coldness of an object Based on average molecular kinetic energy Heat Based on total internal energy of molecules Doubling amount at same temperature doubles heat Flows from high to low temperature

If the temperature of a system is different from its surroundings, then thermal energy is either released or absorbed by the system The “system” includes all associated matter including materials undergoing chemical change. Everything else is known as the “surroundings.” This could be the solvent of a solution, the container, or anything in thermal contact with the container.

How to measure the heat transferred from system to surroundings – using a calorimeter. (Surroundings)

Measures of heat Metric units calorie (cal) - energy needed to raise temperature of 1 g of water 1 degree Celsius kilocalorie (kcal, Calorie, Cal) - energy needed to raise temperature of 1 kg of water 1 degree Celsius English system British thermal unit (BTU) - energy needed to raise the temperature of 1 lb of water 1 degree Fahrenheit Mechanical equivalence J = 1 cal

Specific heat Variables involved in heating Temperature change Mass Type of material –Different materials require different amounts of heat to produce the same temperature change –Measure = specific heat Summarized in one equation

Determining the Quantity of Heat Transferred Heat cannot be measured directly, but heat transfer results in a temperature change. In a calorimeter, we normally measure heat transferred to or from water (the surroundings). To calculate heat (Q) associated with a temperature change of a material, we use the “heat equation,” Q = m∙C∙∆T where, m = mass (in grams) of material, C = specific heat capacity (e.g., cal/g- o C), and ∆T = change in temperature