Where are we going with this? Describe the characteristics of solids, liquids, and gases and changes in state at the macroscopic and microscopic levels.
Endothermic changes (or reactions) take energy IN. The process absorbs energy from it surroundings. Another way to think of this is that energy ENters the system.Exothermic changes (or reactions) give off energy—energy EXits from the system. The process releases energy into its surroundings.
Now, we are going to talk about phase changes from the perspective of the Kinetic Theory of Matter.
So, all matter is made up of particles that are in constant motion. The higher the temperature, the faster they move and, consequently, the higher their kinetic energy.
Got it.
Now, we need to get an idea about what makes something into a solid. Or a liquid. Or… You get the idea.
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Each bond has some amount of energy. You can think of it (metaphorically) like a spring, because that will help with the discussion about what happens that leads to phase changes. Remember, this discussion is, in part, only modelling what happens.
So, picture a solid. To simplify, think in 2 dimensions.
You can think of it as rows and columns of molecules connected by springs. Remember that each of the molecules are moving around (vibrating, if you will, in place) at some rate depending on temperature.
The faster everything shook, the more the springs would stretch out. This is why most things usually expand as the temperature goes up.
Okay… bonds… vibration… temperature… Got it.
In a solid, the kinetic energy of the molecules is less than the energy of the bonds that holds the molecules together in a fixed arrangement.
Thus…
Solids have a definite volumes (at any given temperature)
Solids have a definite shape
The melting phase change occurs at the point where the kinetic energy of the molecules first becomes greater than the energy of the bonds that holds the molecules together in a fixed arrangement.
At this temperature (melting/freezing point), as energy goes into the substance, instead of increasing the kinetic energy of the molecules, it breaks the bonds that hold the substance in a definite shape. The amount of energy needed to break those bonds is called the heat of fusion.
Melting is endothermic.
In a liquid, the kinetic energy of the molecules is greater than the energy of the bonds that holds the molecules together in a fixed arrangement, but less than the energy that holds them into a fixed volume.
Thus…
Liquids have a definite volume (at any given temperature)
Liquids have an indefinite shape.
Vaporization (and Evaporation) occurs when a molecule of a liquid reaches a level of kinetic energy that is greater than the energy that holds liquids in a definite volume.
At this temperature (boiling point), as energy goes into the substance, instead of increasing the kinetic energy of the molecules, it overcomes the attractive forces that give a liquid its definite shape. The amount of energy needed to overcome the attractive forces is called the heat of vaporization.
Vaporization and evaporation are endothermic.
In a gas, although the molecules are still attracted to each other some, the kinetic energy of the molecules is greater than the energy of the bonds that give them a definite shape and greater than the attractive forces that give them a definite volume.
Thus…
Gases have an indefinite volume.
Gases have an indefinite shape.
If the kinetic energy (temperature) keeps going up, the molecules will continue to move faster.
Ionization occurs when the kinetic energy of the molecules is so high that the electrons separate from the nucleus.
Ionization is endothermic.
In a plasma, the kinetic energy is so high that the electrons have separated from the nucleus. It can be thought of that the molecules are moving so fast that the electrons have been shaken off.
Deionization or recombination occurs when molecules decrease in kinetic energy such that the electrons are rejoined to the nucleus.
Deionization / recombination is exothermic.
Condensation occurs when the kinetic energy of molecules decreases to a point less than the energy of the attractive forces that give liquids a definite shape.
Condensation is exothermic.
Freezing occurs when the kinetic energy of molecules decreases to a point less than than the energy of the bonds that give solids their definite volume.
Freezing is exothermic.
Observation is the phenomenon of noticing something and trying to figure out what is going on. Often, observation will populate your mind with questions like "why?" or "how?"
Step 2: Ask Questions
Your observations will probably lead you to wondering something about the thing you noticed.
Questions seek to identify what factors are involved in what is going on in whatever you observed.
For example:
Step 3: Background Research
It's past the first decade of the 21st Century. People do research all the time. It's commonly called "Googling it."
Background Research is finding out what other studies have already uncovered about the observation and your questions.
Researching what others already know can save time, effort, and probably money and materials. If someone has already figured it out, then, unless you notices something is wonky, you can accept the findings and move on—possibly to some other aspect of the observation. Former research can help you revise your question and narrow down what you actually need to know.
Step 4: Construct a Hypothesis
Based on what you are wondering (your question) and the background research, the next step is to come up with a hypothesis.
If your original question from Step 2 was not answered (or was only partly answered) by your research in Step 3, then you can revise your question into a form that can be tested experimentally. This is sort of the launching pad for scientific method. The whole point in making observations and doing research (collecting data) is to be able to formulate a question that can be tested using the scientific method.
Answering the question you come up with becomes the purpose of an experiment. Usually, you'll make a guess at the answer… form a hypothesis.
A formal hypothesis will be a statement that answers a question that relates two or more things. Many times, the question the hypothesis seeks to answer is in the form of:
"What is the relationship between…?"
For instance (back to the first example above in Step 2), you might ask "What is the relationship between age and number of pairs of shoes?"
The hypothesis would be an attempt to answer the question such as:
"As the age of a person goes up, the number of shoes they own goes up as well."
A good hypothesis necessarily includes mention of the things that will be measured or recorded AND the expected relationship between them. There is a name for the thing that will be measured recorded.
A variable in an experiment is something that is recorded or measured. (There are three types of variables: independent, dependent, and controlled. This is a big part of designing an experiment.)
In our example, we would record the age of the subject and measure (count) how many pairs of shoes they have.
The hypothesis implies, by virtue of identifying the variables, how the experiment will be carried out.
Step 5: Design an Experiment
With a good hypothesis ready, the next step is to come up with a systematic process to test the experiment.
A good experiment enables the observation or measurement of the effect of one thing on the other thing (or things) in such a way that everything else is not a factor. This is called controlling all the variables except those related to your hypothesis.
This one little word (controlling) ends up being a huge factor in designing an experiment.
Step 6: Conduct the Experiment and Collect the Data
With a well-designed experiment you can "run" it or "conduct" it and begin collecting data. HOWEVER, sometimes, you get going, and then you have to revise your process, because you discover something isn't working the way you expected.
For example, if you are doing something with how tall people are, and you forget to control for the size of the heels of their shoes, you might have to throw out your data and repeat the process with everyone in bare feet. This would mean going back to Step 5.
Interpreting the Results
So, you asked a question, created a hypothesis, ran the experiment and collected the data. After formulating and objectively testing hypotheses, it is time to interpret the results.
Step 7: Analyze Data
If you had a good hypothesis and a well-designed experiment, this step is easy.
Analyzing the data is the process of looking at the results, sometimes using math and/or statistics, as a way of evaluating if the hypothesis was correct or incorrect.
Think… statistics, graphs, charts, etc.!
Step 8: Draw a Conclusion
Also easy if you have a good experiment. If you hypothesis is stated well, and you obtained good results, then the data will tell you if your hypothesis is correct or not.
Suppose you get data (Step 7) like this:
Take a look at the hypothesis:
"As the age of a person goes up, the number of shoes they own goes up as well."
This did not happen. It happened up until age 30, but then after that, the number of shoes went down. Based on the data collected, the hypothesis is either accepted or rejected. The conclusion of an experiment is tying the data to the hypothesis and stating whether or not the hypothesis can be accepted or rejected.
Step 9: Discussion
The discussion of an experiment addresses anything that wasn't covered. For instance, if you took people from only one income bracket, you might discuss that. The discussion can lead to other questions, such as:
"Is there a difference between the relationship of the number of pairs of shoes and age that depends on income?"
This is a much more complex experiment and data! But this is how science works and how the body of knowledge increases!
The discussion of an experiment addresses limitations to findings and suggests ideas for future research answers a similar or more narrow question.
Summary:
Observation is the phenomenon of noticing something and trying to figure out what is going on.
Step 2: Ask Questions
Questions seek to identify what factors are involved in what is going on in whatever you observed.
Step 3: Background Research
Background Research is finding out what other studies have already uncovered about the observation and your questions.
Step 4: Construct a Hypothesis
A formal hypothesis will be a statement that answers a question that relates two or more things.
A good hypothesis necessarily includes mention of the things that will be measured or recorded AND the expected relationship between them. There is a name for the thing that will be measured recorded.
A variable in an experiment is something that is recorded or measured. (There are three types of variables: independent, dependent, and controlled.
The hypothesis implies, by virtue of identifying the variables, how the experiment will be carried out.
Step 5: Design an Experiment
A good experiment enables the observation or measurement of the effect of one thing on the other thing (or things) in such a way that everything else is not a factor. This is called controlling all the variables except those related to your hypothesis.
Step 6: Conduct the Experiment and Collect the Data
With a well-designed experiment you can "run" it or "conduct" it and begin collecting data. HOWEVER, sometimes, you get going, and then you have to revise your process, because you discover something isn't working the way you expected.
Step 7: Analyze Data
Analyzing the data is the process of looking at the results, sometimes using math and/or statistics, as a way of evaluating if the hypothesis was correct or incorrect.
Step 8: Draw a Conclusion
Based on the data collected, the hypothesis is either accepted or rejected. The conclusion of an experiment is tying the data to the hypothesis and stating whether or not the hypothesis can be accepted or rejected.
Step 9: Discussion
The discussion of an experiment addresses limitations to findings and suggests ideas for future research answers a similar or more narrow question.
Where are we going with this? The information on this page is foundational to science and scientific inquiry.
Science is a system of knowledge about the natural world and the methods used to find that knowledge.
The goal of science is to investigate and understand the natural world (around us) using previous results to make useful predictions.
Science is a system of knowledge about the natural world and the methods used to find that knowledge. It is the intellectual and practical activity encompassing the systematic study of the structure and behavior of the physical and natural world through observation and experiment.
The Scientific method is…
Melting: the process of changing from solid to liquid.Freezing: the process of changing from liquid to solid.Vaporization: the process of changing from liquid to gas at its boiling point.Condensation: the process of changing from gas to liquid.Sublimation: the process of changing from solid to gas.Deposition: the process of changing from gas to solid.Ionization: the process of changing from a gas to a plasma.Recombination/deionization: the process of changing from plasma to gas.
Evaporation is the process that changes a substance from a liquid to a gas at temperatures below the substance's boiling point.
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