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Ch 2 Matter and Energy When ice melts- what happens to its chemical composition?? Name a source of energy for your body. Name some temperature scales. What is a chemical property? Physical property?
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Energy The ability to do work
Always involved with change in matter Physical change- change in matter from one form to another without change in chemical properties
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All physical and chemical changes involve change in energy
Change that occurs when one or more substances change into entirely new substances with different properties All physical and chemical changes involve change in energy Ex. - water Ice (melts) water (evaporates) steam energy energy
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Endothermic Any change in matter in which energy is absorbed
Exothermic Any change in matter in which energy is released
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Law of Conservation of Energy-
Energy cannot be created or destroyed During any physical or chemical change the total quantity of energy remains constant. Energy is transferred between system and surroundings
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Forms of Energy- Chemical, mechanical, light, heat, electrical, & sound Heat- transfer of energy between objects that are at different temperatures Energy can be released or absorbed as heat
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Temperature- Indicated how hot or cold something is
Measurement of kinetic (motion) energy Temp. scale – Celsius- based on freezing point and boiling point of water Kelvin- absolute zero (all particles have minimum kinetic energy) Conversion °C = K
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Transfer of heat may not affect temperature
Transfer of heat may not affect temperature During changes of state – temperatures remain constant Heat of vaporization Heat of fusion
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Scientific Method – A series of steps followed to solve problems, including collecting data, formulating a hypothesis, and stating conclusions
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Hypothesis- theory or explanation that is based on observations and that can be tested. Variable- A factor that could affect the results of an experiment Controlled experiment- only one variable
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Data- recorded observations and or measurements
Theory- an explanation for some phenomenon that is based on observation, experimentation and reasoning Law- a summary of many experimental results and observations, a law tells how things work Ex. Law of conservation of mass – products of a reaction must have the same mass as the reactants
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Models- represent an object, a system, a process, or an idea
Simpler than actual thing Useful to understand what happens at microscopic and submicroscopic level
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Measurements and calculations-
Accuracy- description of how close a measurement is to the true value of the quantity measured Precision- the exactness of a measurement
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Significant figures- A prescribed decimal place that determines the amount of rounding off to be done based on the precision of the measurement Rules p 57 in text
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Sig figs con’t There are 3 digits in this measurement- two you are sure of (16) and one estimate (.1) these are the three significant figures Significant figures are all the digits we are sure of plus one that is estimated.
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Specific Heat- Quantity of energy that must be transferred as heat to raise the temp of 1 gram of a substance by 1 K Table p 60 in text calculation p 61 follow process!!!!
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Calculating Specific heat- A 4
Calculating Specific heat A 4.0 g sample of glass was heated from 274 K to 314 K and was found to absorb 32 J of energy as heat. Calculate the specific heat of glass. 1 2 3 4 Gather information Plan your work Calculate Verify your results Mass = 4.0 g Energy (q) = 32 J initial temp = 274 K final temp = 314 K T = final temp – initial temp Cp = m x T q Cp = g x (40 K) 32 J Check Units & sig figs = J/g -K
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Scientific Notation-All numbers in scientific notation have 2 parts – first part is between 1-10 but has any number of digits as decimals- second part is a power of ten expressed as an exponent This is a number written as Scientific Notation. The Standard Form is
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