Unit 7: Thermochemistry

difference between heat and temperature

Heat is the transfer of thermal energy between two bodies that are at different temps (also includes totally energy and mass) and temperature is actually our way of measuring the average kinetic energy of the participles in a sample

Endothermic

Heat is transferred from the surroundings to the system, enthalpy is positive, products are higher in energy than the reactants

Exothermic

heat is lost from the system and transferred to the surroundings, enthalpy is negative, products are lower in energy than the reactants

2 proper units for heat energy are

KJ and K calories

Temperature is usually measured in

Celsius

Specific heat capacity means

Amount of energy needed to raise one gram of a substance by one degree Celsius

Kinetic energy is the energy of motion which can be measured with ___changes in state usually involve a change ___energy

Temperature and potential

True to false: heat lost is equal to heat gained during a chemical reaction

True

Calorímetry

Measuring the amount of heat absorbed or lost during a chemical reaction

_____(triangle H) is the heat change for a chemical reaction

Enthalpy change

How to calculate energy associated with a temperature change

Q = m c triangle T

How to calculate energy associated with a phase change

Q = n triangle H

How to use specific heat capacity to explain why some substances change temperature more rapidly than others when exposed to the same environment

High specific heat substances (water) require more energy. Substances with low specific heat (metals) require little energy to change temperature, heating and cooling

Explain how to minimize experimental error in calorimetry experiment

Maintain insulation to use high prevent heat precision thermometers

Determine which substances would be best to use for a hot pack vs cold pack based on the enthalpy of their reactions

• hot packs (exothermic) negative enthalpy change meaning they release heat into surroundings water when dissolved

• Cold packs (endothermic) require substances, postive enthalpy change, meaning they absorb heat from the surroundings (water) when dissolved

Fusion

The phase change between solid and liquid

vaporization

phase change between liquid and gas

sublimation

the phase change between solid and gas

Formation

making of a compound from its elements

reaction

the reaction as it is written

enthalpy H

is a term that describes the amount of energy per amount of material

what are the usual units for enthalpy

kI/mole or kJ/gram

what is considered standard state?

0 C or 273 K (temp), 1 atm (pressure) and 1 M (concentration)

How is standard state different from standard temperature and pressure (STP)?

Concentration isn’t given for STP BUT we know that for any gas at STP, 1 mol gas = 22.4 L

1 cal =

4.184 J

1000 joules =

1 kJ

food calories are…

kilocalorie so 1 calorie =4.184 joules 1000 calories

Specific heat of steam

2.01

specific heat of solid water

2.01

specific heat of water

4.184

heat of fusion

6.01

heat of vaporatzation

40.67

heat always flows

from substance at a higher temperatures to a substance at a lower temperature until same temperature (thermal equilibrium) ‘’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’

Kelvin

273.15 degrees from C

The system

specific part of the universe that we study in

The surroundings

are the rest of the universe

the universe

the system and surroundings

open system

heat and matter can be exchanged

closed system

Heat can be exchanged

No heat or matter exchanged

Isolated system

does heat change while the heating curve is flat

yes heat breaks apart IMFS

does temperature change while the heating curve is flat?

no heat goes to break IMFS