Chemistry notes
Lecture 12 Chapter 6
6.1 Thermochemistry: Energy & units (p.227)
From observation we know, that
- some chemical reactions begin as soon as the reactants come into contact with each other (precipitation reactions)
- some reactions are slow or even so slow at room temperature that even lifetime is not enough to observe a measurable change (rusting of iron, tarnishing silver)
Also, almost all chemical reactions involve exchange of heat (or energy): in combustion reactions great deal of heat is released in neutralization reactions and others.
Transfer of heat is a major theme of thermodynamics, the science of heat exchange (or energy exchange).
Q: Why it is important to know the quantity of heat (energy) involved in a chemical reaction?
Answer: when chemical reaction takes place the rearrangement of atoms takes place and some bonds have to be broken (energy is needed) and new bonds form (energy is released) we can learn about the strength of the bonds, we can also predict whether the reaction will occur.
Q: How to define energy? or What is energy?
Energy is capacity to do work. (or ability to do work)
Unlike matter, energy is known and recognized by its effect. It cannot be seen, touched, smelled, or weighed.
Different forms of energy:
Kinetic energy, Ek: energy associated with the moving object, it can be calculated, if we know the mass of an object and it speed or velocity
Ek = m v2 units of energy: kg x m2/s2 is called joule (J) Examples of kinetic energy: energy of moving baseball electric energy of electrons moving through a conductor radiant energy from the sun thermal energy of atoms, molecules ,or ions at the submicroscopic level
Kinetic energy is often expressed by common unit of energy, that is by calorie (cal)
1 calorie is the amount of energy needed to raise the temperature of one gram of water, H2O, by one oC. 1 cal = 4.184 J
Potential energy, Ep:
6.1 Thermochemistry: Energy & units (p.227)
From observation we know, that
- some chemical reactions begin as soon as the reactants come into contact with each other (precipitation reactions)
- some reactions are slow or even so slow at room temperature that even lifetime is not enough to observe a measurable change (rusting of iron, tarnishing silver)
Also, almost all chemical reactions involve exchange of heat (or energy): in combustion reactions great deal of heat is released in neutralization reactions and others.
Transfer of heat is a major theme of thermodynamics, the science of heat exchange (or energy exchange).
Q: Why it is important to know the quantity of heat (energy) involved in a chemical reaction?
Answer: when chemical reaction takes place the rearrangement of atoms takes place and some bonds have to be broken (energy is needed) and new bonds form (energy is released) we can learn about the strength of the bonds, we can also predict whether the reaction will occur.
Q: How to define energy? or What is energy?
Energy is capacity to do work. (or ability to do work)
Unlike matter, energy is known and recognized by its effect. It cannot be seen, touched, smelled, or weighed.
Different forms of energy:
Kinetic energy, Ek: energy associated with the moving object, it can be calculated, if we know the mass of an object and it speed or velocity
Ek = m v2 units of energy: kg x m2/s2 is called joule (J) Examples of kinetic energy: energy of moving baseball electric energy of electrons moving through a conductor radiant energy from the sun thermal energy of atoms, molecules ,or ions at the submicroscopic level
Kinetic energy is often expressed by common unit of energy, that is by calorie (cal)
1 calorie is the amount of energy needed to raise the temperature of one gram of water, H2O, by one oC. 1 cal = 4.184 J
Potential energy, Ep: