Energy conservation and transformation
Energy conservation and transformation
Law of conservation—> requires that energy is neither created nor destroyed
—> it can only change forms, such as from potential energy to kinetic energy, or from chemical energy to thermal energy.
When energy is transferred or transformed from one system to another, all energy can be accounted for
Ex: In a campfire, the chemical energy from the fuel is converted into thermal energy (heat), light energy, and sound energy (sound). The equation that represents this chemical energy (imput) is typically expressed as: ( C_xH_y + O_2 \rightarrow CO_2 + H_2O + energy ), where the reactants are the fuel and oxygen, and the products are carbon dioxide, water, and the energy released during the reaction.
Specific Heat
Q is the amount of heat energy absorbed or released in a process, which can be calculated using the formula Q = mcΔT, where m is the mass of the substance, c is the specific heat capacity, and ΔT is the change in temperature.
Q: Calculate the heat energy required to raise the temperature from 5C to 10 C. The specific heat of water is 4.184 j/coules (J). Using the formula, we have Q = mcΔT = (1 kg)(4.1 J/kg°C)(10°C - 5°C) = 20.5 J.
What is specific heat capacity? - The amount of energy needed to raise the temperature of 1 kg of material by 1 degree K
How does specific heat capacity affect the rate of temperature change of a substance? The higher the specific heat capacity, the more energy is required to change the temperature of the substance, resulting in a slower rate of temperature change when energy is added or removed.
Forces and energy
-Force equals mass times acceleration (F=ma)
acceleration is the change in velocity per change in time
-Force exerts in equal and opposite directions. The energy that is lost is converted in heat
Electrical forces at Atomic scales
-Opposites attract
protons and electrons are attracted to each other
-Like charges repel
positives repel each other
negatives repel each other
Endothermic and exothermic reactions
Exothermic= heat is released to the surroundings because the reaction products are at a lower energy level than the reactants. (Ex- heat packs)
Endothermic= heat is absorbed from the surroundings because the reaction products are at a higher energy level than the reactants
How can you identify wether a reaction is endothermic or exothermic by observing temperature changes?
If the temperature of the surroundings decreases, the reaction is likely endothermic; if it increases, the reaction is likely exothermic. The ability to identify these reactions is crucial in fields such as chemistry, biology, and environmental science, where energy changes are fundamental to understanding processes.
-Heat flows from warmer to cooler objects, the greater the difference, the faster the heat flows
Activation energy-the minimum energy colliding particles must have in order to react
-reactions with low activation energies happen easily and quickly
Ex: since sodium is reactive, it only needs a little activation energy.
Open and closed systems
Thermochemistry- study of heat exchanges between systems and their surroundings.
Matter and energy conservation in combustion
-Oxygen gas reacts with a molecule, releasing energy in both heat and light (a flame)
-Matter is conserved during reaction
dependent on amount of oxygen present
Complete combustion
-with sufficient oxygen, complete combustion of propane produces water, carbon dioxide, and energy, energy from the reaction is transferred to the pot of water on the burner
Thermal energy and kinetic energy
During this process, thermal energy heats the water, while kinetic energy increases the movement of water molecules, leading to higher temperatures and eventually boiling.
As the water reaches its boiling point, the kinetic energy continues to rise, causing the water to transition into steam, which signifies a change in state from liquid to gas.
total thermal energy of a system depends on the temperature, number of atoms, in a system and the state of the material.
Thermal conduction
-occurs through the oscillations of adjacent atoms
-energy will pass from the hotter to the cooler atoms
Thermal conductivity- measure how efficiently heat is conducted through a material
Insulators- materials with very low thermal conductivities
Convection- cycling of fluid materials. drive by differences in density
Entropy
Entropy- measure of the disorder of a system- the opposite of the order of the system
-Entropy of an isolated system never decreases
-the second law of thermodynamics-a system that always spontaneously evolves toward the state with the maximum entropy
This means that energy transformations are not 100% efficient, as some energy is always lost to disorder.
Thermal equilibrium- heat is no longer flowing between systems, resulting in a stable distribution of energy.
Bohr model
Ground state- electron in the lowest possible energy level
Excited State- electron has gained energy and in a higher energy level
Emission spectrum lines- each spectral line has a specific wavelength and is for one electron transition to a lower energy level
Energy level in atoms- represents these energies with orbits with differing distances from the nucleus
Innermost orbit corresponds to the lowest energy an electron can have
Second energy level corresponds to the next highest energy, can represents up to eight electrons