Chemical Reactions
What is the difference between exothermic and endothermic reactions?
Energy is released in an exothermic reaction and absorbed in an endothermic reaction.
Does the identity of a substance change during a physical change?
No, the identity stays the same because the substance stays the same.
What is one property that can be used to identify a substance (it is unique to a pure substance)
Density
A log of wood burning is what kind of energy?
Thermal
What property does not tell us the identity of a substance.
Mass
What is some evidence of a chemical reaction occuring?
A change in color, energy being released as heat, the formation of different-colored solids.
Water being boiled is an example of a physical change? True or False
True
Two clear, colorless liquids look exactly the same. A student measures their densities and finds that one has a density of 1.0 g/mL and the other has a density of 1.3 g/mL.
What can the student conclude?
The liquids are different substances because they have different densities.
In what direction does thermal energy flow?
Thermal energy flows from hot objects towards cold objects.
What are 2 physical properties of substances that can help identify an unknown substance
Density and Melting Point
Why do products have different properties than reactants?
Products have different properties than reactants because they are new substances with different characteristics.
What are two physical properties we can use to identify pure substances?
Density and Melting Point
What happens to the reactants in a chemical reaction?
They regroup to form new substances
What is heat?
the transfer of thermal energy from one object to another.
What are 2 chemical properties of substances that can help identify an unknown substance?
Flammability and Reactivity
How can you tell that a chemical equation is balanced?
There are the number of each type of atom on both sides of the chemical equation.
How do the atoms compare before and after a physical change?
The atoms of a substance remain the same in number, type, and arrangement, meaning no new substances are formed.
A student finds two metals that look the same. When placed in water, one sinks quickly while the other floats just below the surface. Which property could the student use to identify which metal each one is?
Density
What is temperature?
The average kinetic energy of particles in a substance.
describe the flow of energy as rock salt is dissolved in water
Energy is absorbed by the reaction, and the temperature of the surroundings decreases.
Is photosynthesis an example of an exothermic or endothermic reaction?
Endothermic reaction
the type of particles it contains (atoms or molecules) and how those particles are arranged and bonded.
A student discovers two shiny metal samples that look nearly identical. When placed near a magnet, one is attracted, but the other is not. Which property should the student use to tell the metals apart?
If during a chemical reaction the final temperate is lower than the initial temperature, then what are the inputs and outputs?
The inputs are reactants and energy ; the outputs are products only.
What might have happened to the remaining mass of a substance when it appears to have disappeared?
Some of the atoms were rearranged to form a gas.