Ch.17: Reaction Energy and Reaction Kinetics Introduction to Thermochemistry

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

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

Heat Transfer

Heat measured using a calorimeter (reaction container that is surrounded by water) 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 mass of material size of T change specific heat: (cp) the amount of energy required to raise the T of one gram of substance by one °C

Specific Heat measured under constant pressure

Why does water have such a high specific heat? water metal Water molecules form strong bonds with each other; therefore it takes more heat energy to break them. Metals have weak bonds and do not need as much energy to break them.

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 4.184 J/g°C.

Example Aluminum has a specific heat of 0.900 J/g°C and water has a specific heat of 4.18 J/g°C. How high must the temperature of the aluminum be to cause the water temperature to raise from 22°C to 28°C? You are using 25 g of aluminum and 50. grams of water. T = 84°C