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Chem2: Matter & Energy
Transcript of Chem2: Matter & Energy
Apply the law of conservation of energy.
Distinguish between heat and temperature.
Convert between Celsius and Kelvin.
Use the scientific method.
Differentiate between a hypothesis, a theory, and a law.
Differentiate between accuracy and precision.
Use significant figures and scientific notation.
Calculate energy changes using specific heat.
Scientific Method- A specific set of procedures for conducting research
Hypothesis- A proposed explanation of observations
Theory- A hypothesis that withstands repeated testing and makes testable predictions
Law- A statement or mathematical expression that reliably describes the behavior of the natural world
Law of Conservation of Mass- The products of a chemical reaction have the same mass as the reactants have
Energy- The capacity to do some kind of work
(i.e. moving an object, forming a new compound,
Physical Change- When a state of matter is only
affected physically (i.e. ice melting, water boiling)
Chemical Change- When a new substance is formed
from a chemical reaction
Evaporation- The process where liquid water is
heated enough up to its boiling point, at which
point it turns into gas
Endothermic Process- Any change in matter
in which energy is absorbed
Exothermic Process- Any change in matter
in which energy is absorbed
Law of Conservation of Energy- During any physical or
chemical change, the total quantity of energy remains
Heat- Energy transferred between objects
that are at different temperatures
Kinetic Energy- Energy that is "in motion"
or being used
Temperature- A measurement of the average
kinetic energy of the random motion of particles
in a substance
Specific Heat- The relationship between energy
transferred as heat to a substance and the substance's temperature change
Studying Matter and Energy
Heat is always transferred from the warmer object to the cooler object.
Two scales are used to measure temperature in chemestry: Kelvin and Celsius.
The SI unit of temperature is the Kelvin. 0 Kelvins (absolute zero) is the lowest possible temperature.
To convert Kelvins to degrees Celsius, subtract 273. To convert degrees Celsius to Kelvins, add 273.
A transfer of heat doesn't always cause a change in temperature.
Different substances have different specific heats. A substance's specific heat is the amount of energy required to raise the temperature of 1 gram by 1 Kelvin, measured as joules/gram kelvin.
Scientists must form a hypothesis (a guess as to why something happens) from observations they have made. Then, they must test this hypothesis with experiments.
In an experiment, all possible variables must be identified and tested individually in order to determine the exact cause of a given occurrence.
Data from experiments, if consistent and reliable, can become a theory (an explanation for a phenomenon based and observation and testing).
A theory explains why events occur, whereas a law describes the events themselves.
The law of conservation of mass tells us that mass is not created or destroyed.
Scientists often use models (simplified representations of objects, systems, processes, or ideas) to clearly illustrate a point.
Measurements and Calculations in Chemistry
Scientific notation is used to more easily represent very large and very small numbers.
The first part of a number written in scientific notation is a number between 1 and 10 with any number of digits after the decimal point. There should only be one digit to the left of the decimal point.
The second part of a number written in scientific notation is a power of 10, written as an exponent. The value of the exponent is the number of places the decimal point was moved until there was just one digit to the left. If the decimal point was moved to the left, the exponent is positive. If the decimal was moved to the right, the exponent is negative.
Rules for using scientific notation: 1. In scientific notation, exponents are count values. 2. In addition and subtraction problems, all values must have the same exponent before they can be added or subtracted. 3. In multiplication problems, the first factors of the numbers are multiplied and the exponents of 10 are added. 4. In division problems, the first factors of the number are divided and the exponent of 10 in the denominator is subtracted from the exponent of 10 in the numerator.
Rules for scientific notation with significant figures: 1. Use scientific notation to eliminate all place-holding zeros. 2. Move the decimal in an answer so that only one digit is to the left, and change the exponent accordingly. The final value must contain the correct number of significant figures.
Energy and Change
Matter and energy, like any other field of science, is studied with the scientific method (see graphic).
Rational thought and logic are not enough in science. Ideas must be tested through experiments.
Experiments often do not turn out as expected. If this occurs, the scientist must revise their hypothesis and try again.
Discoveries are often made by chance or by accident.
The Scientific Method
Calculations are often not exact, as all measurements are subject to such things as human error, method error, or limitation of the instruments used.
Scientists will repeat their calculations several times to avoid incorrect data. The goal is for the data to have been measured with precision and accuracy.
The right equipment is essential to making accurate and precise measurements.
A measurement's accuracy is its proximity to the correct quantity.
Precision refers to how close multiple measurements of the same quantity are to each other.
Accuracy and Precision
Significant figures (all of the digits that are certain in a measurement as well as one estimated digit at the end) show how precise a measurement is.
Rules for determining significant figures: 1. Nonzero digits are always significant. 2. Zeros between nonzero digits are significant. 3. Zeros in front of nonzero digits are not significant. 4. Zeros both at the end of a number and to the right of a decimal point are significant. 5. Zeros both at the end of a number but to the left of a decimal point may not be significant. If a zero has not been measured or estimated, it is not significant. A decimal point placed after zeros indicates that the zeros are significant.
Calculators do not identify significant figures.
Rules for using significant figures in calculators: 1. In multiplication and division problems, the answer cannot have more significant figures than there are in the measurement with the smallest number of significant figures. 2. In addition and subtraction of numbers, the result can be no more certain than the least certain number in the calculation. 3. If a calculation has both addition (or subtraction) and multiplication (or division), round after each operation.
Exact values, such as count values and conversion factors, have unlimited significant figures.
Measuring Specific Heat
To measure a substance's specific heat at a given pressure, divide the energy transferred as heat by the the product of the mass of the substance and the change in temperature.
Accuracy: A description of how close a measurement is to the true value of the quantity measured
Precision: The exactness of a measurement
Significant Figures: A prescribed dcimal place that determines the amount of rounding off to be done based on the precision of the measurement
Scientific Notation: A two-part way of writing very large or very small numbers
Superheavy elements, those whose atomic
number is greater than 106, are often created
with synchrotrons. However, they only last for
a very short time - normally only a fraction of
a second. The US, Germany, Russia, and Sweden
are among the nations with the resources to carry
out research into superheavy elements.
Energy is always involved when there is a change in matter.
Changes in matter can be physical (different form, same properties), or chemical (entirely new substance with different properties).
Changes in matter can either involve a gain in energy (solid to liquid, liquid to gas) or a release of energy (gas to liquid, liquid to solid).
When energy is absorbed in a process, the process is endothermic. When energy is released in a process, the process is exothermic.
The law of conservation of energy tells us that, during a physical or chemical change, the total quantity of energy involved remains constant (energy is not created or destroyed).
During a change in matter, energy is transferred back and forth between a system and its surroundings.
Forms of energy include chemical, mechanical, light, heat, electrical, and sound.