Chapter 10
The Nature of Energy
- energy- ability to do work or produce heat
- potential energy- energy due to position of composition; example: water behind a dam has potential energy
- kinetic energy- an object is energy due to the motion of the object and depends on the mass of the object m and its velocity v
equation: KE= 1/2(mv^2)
- law of conservation of energy- energy that can be converted from one form to another but can not be neither created nor destroyed
- force- force acting over a distance
- state function- a property of the system that changes independently or its pathway
- potential energy- energy due to position of composition; example: water behind a dam has potential energy
- kinetic energy- an object is energy due to the motion of the object and depends on the mass of the object m and its velocity v
equation: KE= 1/2(mv^2)
- law of conservation of energy- energy that can be converted from one form to another but can not be neither created nor destroyed
- force- force acting over a distance
- state function- a property of the system that changes independently or its pathway
Temperature and Heat
- temperature- measure of the random motions of the components of a substance
- heat- a flow of energy due to a temperature difference
- the flow of energy called heat is the way in which thermal energy is transferred from a hot object to a colder
- heat- a flow of energy due to a temperature difference
- the flow of energy called heat is the way in which thermal energy is transferred from a hot object to a colder
Exothermic and Endothermic Processes
- system- the part of the universe on which we wish to focus attention
- surroundings- include everything else in the universe
- exothermic-a process that results in the evolution of heat; energy flows out of the system as heat
- endothermic- process that absorbs energy from the surroundings; when heat flow moves into a system
- the energy gained by surroundings must be equal to the energy lost by the system
- in any exothermic reaction, some of the potential energy stored in the chemical bonds is converted to thermal energy (random kinetic energy) via heat
- surroundings- include everything else in the universe
- exothermic-a process that results in the evolution of heat; energy flows out of the system as heat
- endothermic- process that absorbs energy from the surroundings; when heat flow moves into a system
- the energy gained by surroundings must be equal to the energy lost by the system
- in any exothermic reaction, some of the potential energy stored in the chemical bonds is converted to thermal energy (random kinetic energy) via heat
Thermodynamics
- thermodynamics- study of energy
- first law of thermodynamics (law of conservation of energy)- energy of universe is constant
- internal energy- sum of the kinetic and potential energy of all the 'particles' in the system; it can change by a flow of work, heat, or both
equation- change in E = q + w
- q represents heat
- w represents work
- thermodynamic quantities always consist of two parts: a number, giving the magnitude of the change, and a sign, indicating the direction of the flow
- the sign reflects the system's point of view
- when energy flows into system via heat (endothermic process) q= +x, a positive sign shows energy is increasing
- when energy flows out of system via heat (exothermic process) q= -x, a negative sign shows energy is decreasing
- first law of thermodynamics (law of conservation of energy)- energy of universe is constant
- internal energy- sum of the kinetic and potential energy of all the 'particles' in the system; it can change by a flow of work, heat, or both
equation- change in E = q + w
- q represents heat
- w represents work
- thermodynamic quantities always consist of two parts: a number, giving the magnitude of the change, and a sign, indicating the direction of the flow
- the sign reflects the system's point of view
- when energy flows into system via heat (endothermic process) q= +x, a positive sign shows energy is increasing
- when energy flows out of system via heat (exothermic process) q= -x, a negative sign shows energy is decreasing
Measuring Energy Changes
- calorie- the amount of energy required to raise the temperature of one gram of water by one Celsius degree
- joule- can be conveniently defined in terms of calorie: 1 cal = 4.184 J
- problem: express 60.1 cal of energy in units of joules
- joule- can be conveniently defined in terms of calorie: 1 cal = 4.184 J
- problem: express 60.1 cal of energy in units of joules
- problem- determine the amount of energy needed to increase the temperature of 7.40 g water from 29.0 degrees C to 46.0 degrees C
- energy required to change the temperature of substance depends on:
1. the amount of substance being heated (number in grams)
2. the temperature change (number of degrees)
- specific heat capacity- amount of energy required to change the temperature of one gram of a substance by one degree Celsius degree
- equation:
1. the amount of substance being heated (number in grams)
2. the temperature change (number of degrees)
- specific heat capacity- amount of energy required to change the temperature of one gram of a substance by one degree Celsius degree
- equation:
- problem- what quantity of energy is required to heat a piece of iron weighing 1.3 g from 25 degrees C to 46 degrees C? (C=.45 J/g degrees C) what is the answer in calories?
For more help with specific heat capacity, watch this video
Test your knowledge with these specific heat quiz
Test your knowledge with these specific heat quiz
Thermochemistry (Enthalpy)
- enthalpy- shows how much energy is produced and absorbed by a given reaction
- change in enthalpy is equal to the energy that flows as heat
-problem- when 1 mole of methane is burned at a constant pressure, -890 kJ of energy is released as heat. calculate the change in enthalpy for a process in which a 5.8 g sample of methane is burned at a constant pressure
- change in enthalpy is equal to the energy that flows as heat
-problem- when 1 mole of methane is burned at a constant pressure, -890 kJ of energy is released as heat. calculate the change in enthalpy for a process in which a 5.8 g sample of methane is burned at a constant pressure
- calorimeter- device used to determine the heat associated with a chemical reaction
Hess's Law
- the change in enthalpy for a given process is independent of the pathway for the process
- Hess's Law- in going from a particular set of reactants to a particular set of products, the change in enthalpy is the same whether the reaction takes place in one steps or a series
- to understand Hess's Law to compute enthalpy changes, it is important to understand two characteristics of a change in enthalpy for a reaction:
1. if a reaction is reversed, the sign of change in enthalpy is also reversed
2. magnitude of change in enthalpy is directly proportional to the quantities of reactants and products in a reaction. if the coefficients in a balanced reaction are multiplied by an integer, the value of change in enthalpy is multiplied by that integer
- problem:
- Hess's Law- in going from a particular set of reactants to a particular set of products, the change in enthalpy is the same whether the reaction takes place in one steps or a series
- to understand Hess's Law to compute enthalpy changes, it is important to understand two characteristics of a change in enthalpy for a reaction:
1. if a reaction is reversed, the sign of change in enthalpy is also reversed
2. magnitude of change in enthalpy is directly proportional to the quantities of reactants and products in a reaction. if the coefficients in a balanced reaction are multiplied by an integer, the value of change in enthalpy is multiplied by that integer
- problem:
For more practice with Hess's Law watch this video
For more information on Hess' Law go to this website
For more information on Hess' Law go to this website
Quality Versus Quantity of Energy
- one of the most important characteristics of energy is that it is conserved
- 'energy crisis' is not about the quantity of energy, but rather about the quality of energy
- when we use energy the quality of that energy (its ease of use) is lowed
- petroleum is highly valuable because it furnishes a convent, concentrated source of energy
- unfortunately, we are using this fuel at a much faster rate than natural processes can replace it
- logical energy source: sun
- solar energy- refers to using the sun's energy directly to produce work in our society
- 'energy crisis' is not about the quantity of energy, but rather about the quality of energy
- when we use energy the quality of that energy (its ease of use) is lowed
- petroleum is highly valuable because it furnishes a convent, concentrated source of energy
- unfortunately, we are using this fuel at a much faster rate than natural processes can replace it
- logical energy source: sun
- solar energy- refers to using the sun's energy directly to produce work in our society
Energy and Our World
- by process of photosynthesis, plants store energy that can be claimed by burning the plants themselves or the decay products that have been converted over millions of years to fossil fuels
petroleum and natural gas
- petroleum- thick, dark liquid composed mostly of compounds called hydrocarbons that contain carbon and hydrogen
- natural gas- usually associated with petroleum deposits; consists mostly of methane and contains ethane, propane, and butane
coal
- coal- formed from remains of plants that were burned and subjected to high pressure and hear over long periods of time
- coal 'matures' through four stages: lignite, sub bituminous, bituminous, and anthracite
- each stage has a high carbon-to-oxygen and carbon-to-hydrogen ratio
- coal is plentiful/important US; furnishing approximately 20% of our energy
- coal is expensive/dangerous to mine
- burning coal yields air pollutants and can lead to acid rain
effects of carbon dioxide on climate
- earth receives a lot of energy from sun (30%) which is reflected by earth's atmosphere
- remaining energy passes through atmosphere to earth surface
- energy absorbed by plants for photosynthesis and ocean
- most absorbed by soil and rocks, increasing earth's temperature
- infrared radiation- energy radiated from heated surface
- greenhouse effect- atmosphere is transparent to visible light and absorbs infrared radiation, raising the temperature
petroleum and natural gas
- petroleum- thick, dark liquid composed mostly of compounds called hydrocarbons that contain carbon and hydrogen
- natural gas- usually associated with petroleum deposits; consists mostly of methane and contains ethane, propane, and butane
coal
- coal- formed from remains of plants that were burned and subjected to high pressure and hear over long periods of time
- coal 'matures' through four stages: lignite, sub bituminous, bituminous, and anthracite
- each stage has a high carbon-to-oxygen and carbon-to-hydrogen ratio
- coal is plentiful/important US; furnishing approximately 20% of our energy
- coal is expensive/dangerous to mine
- burning coal yields air pollutants and can lead to acid rain
effects of carbon dioxide on climate
- earth receives a lot of energy from sun (30%) which is reflected by earth's atmosphere
- remaining energy passes through atmosphere to earth surface
- energy absorbed by plants for photosynthesis and ocean
- most absorbed by soil and rocks, increasing earth's temperature
- infrared radiation- energy radiated from heated surface
- greenhouse effect- atmosphere is transparent to visible light and absorbs infrared radiation, raising the temperature
Energy as a Driving Force
- energy spread- concentrated energy is dispersed widely; happens every time in an exothermic process
- matter spread- molecules of a substance are spread out and occupy a larger volume
entropy
- entropy- keep track of natural tendency for the components of the universe to become disordered
- as randomness increases, entropy increases
- second law of thermodynamics- entropy of universe is alway increasing
- spontaneous process- occurs in nature without outside intervention; helps us understand why certain processes are spontaneous or not
- matter spread- molecules of a substance are spread out and occupy a larger volume
entropy
- entropy- keep track of natural tendency for the components of the universe to become disordered
- as randomness increases, entropy increases
- second law of thermodynamics- entropy of universe is alway increasing
- spontaneous process- occurs in nature without outside intervention; helps us understand why certain processes are spontaneous or not