Chemical reactions and thermochemistry Flashcards
Energy is the ability to do work. What is the equation for work?
Work = Force x Distance
Name types of energy
- Potential energy
- Kinetic energy
- Electromagnetic
- Nuclear
- Chemical energy
What is the first law of thermodynamics?
Law of conservation of energy the energy of the universe is constant
Define Internal energy
The sum of the kinetic and potential energies of all particles in the system. It can be changed by a flow of work, heat or both. ΔE = q + w
State key facts about enthalpy
- Internal energy
- A measure of the heat content of a substance at constant pressure
- You can’t measure the actual enthalpy of a substance (You can measure enthalpy CHANGE)
When is a reaction exothermic or endothermic?
- Enthalpy of reactant > products, ∆H negative (Exothermic - heat given out)
- Enthalpy of reactants < products, ∆H positive (Endothermic - heat absorbed)
Define Exothermic and endothermic reactions
Exothermic - heat is released by the reaction
Endothermic - heat is consumed by the reaction
What is the standard enthalpy of formation?
~ The standard enthalpy of formation or a pure element in its standard state is defined as zero ~
State the equation for enthalpy change
Enthalpy change = mass x heat capacity x temperature change
What is the Hess’ Law
The heat change of a whole reaction is equivalent to the sum of heat changes in its steps
Breaking bonds is…..
Making bonds is…..
- endothermic (positive value)
- exothermic (negative value)
What is the law of thermodynamics ||?
Entropy will always tend to increase. Heat will always flow from a high temperature to a lower temperature
What is the law of thermodynamics |||?
Entropy is temperature dependant. If all the thermal motion of molecules (kinetic energy) could be removed, a state called absolute zero would occur
~ Absolute zero = 0 kelvin = -273.15 degrees celsius
What does entropy measure?
• Measures the amount of energetic disorder in a system
- the greater the disorder of the particles in a substance or mixture, the higher the entropy
What is an example of entropy increasing?
~ Solids Melting
~ liquids boiling
~ number of molecules increasing
(all spontaneously occurring chemical and physical changes involve an overall increase in entropy)
