Ch.1: Matter and Change Introduction to Thermochemistry

Introduction  Thermochemistry: study of transfers of energy as heat occurring during chemical and physical changes study of transfers of energy as heat occurring during chemical and physical changes  Temperature: (T) average kinetic energy of the particles in a sample average kinetic energy of the particles in a sample as kinetic energy increases, so does temperature as kinetic energy increases, so does temperature as temperature increases, KE increases as temperature increases, KE increases

Heat  (q) energy transferred between samples because of their difference in T  moves spontaneously from matter with higher T to matter with lower T  amount of energy transferred is measured in Joules (J)  heat can’t be measured directly so T is used to track transfer of heat

Heat Transfer

Heat  measured using a calorimeter (reaction container that is surrounded by water) calorimeter  the energy given off during a reaction is equal to the energy absorbed by the water

Two Types of Calorimeters

Specific Heat  the amount of energy transferred during a temperature change depends on: type of material type of material mass of material mass of material size of T change size of T change  specific heat: (c) the amount of energy (q) required to raise the T of one gram of substance by one °C

Specific Heat  measured under constant pressure

Example A 4.0 g sample of glass was heated from 274 K to 314 K and was found to have absorbed 32 J of energy.  Find the specific heat of the glass sample.

Example  How much energy will the same glass sample gain when heated from 314 K to 344 K?

Example  If 200. g of water at 20°C absorbs 41,840 J of heat, what will its final T be? The specific heat of water is J/g°C.

Example

Example  Aluminum has a specific heat of J/g°C. How much energy in kJ is needed to raise T of 635 g block from 30.7°C to 82.1°C?