General Chemistry
Which of the following is an example of an EXOTHERMIC reaction?
Photosynthesis: Carbon dioxide + Water + Energy → Glucose + Oxygen
Burning wood: Fuel + Oxygen → Carbon dioxide + Water + Energy
Burning wood: Fuel + Oxygen → Carbon dioxide + Water + Energy
Which of the following shows signs of a chemical reaction?
A. a colorless liquid and a gray solid are mixed to produce a gas and a green liquid
B. liquid water is boiled to produce steam
a colorless liquid and a gray solid are mixed to produce a gas and a green liquid
What is the key difference between a physical change and a chemical change?
The main difference between a physical change and a chemical change is what happens at the molecular level. In a chemical change, the atoms within molecules are rearranged and a new substance is formed. Examples include burning wood where the wood reacts with oxygen and ash is formed and fireworks combusting. With a physical change, the materials only change in appearance, but are still made of the same substances. For example, cutting paper, breaking a pencil, and salt dissolving in water.
A clear liquid at room temperature is added to some white powder, also at room temperature. The mixture fizzes and bubbles. The temperature of the mixture increases from 20 ℃ to 50 ℃. Did a new substance form?
Yes, a new substance was formed.
No, a new substance was not formed.
Mass cannot be created or destroyed during a chemical reaction, it is only rearranged. What is this law referred to?
Law of Conservation of Mass
Ammonia is chemically notated as: NH3. How many different elements make up this molecule?
2 elements: Nitrogen and Hydrogen
A student pours two different liquids into a glass beaker. Which of the following would indicate that a chemical reaction occurred between the two liquids?
A. an increase in total mass of the liquids
B. the formation of a solid in the beaker
B. the formation of a solid in the beaker.
What is the difference between reactants and products?
Reactants are the starting substances of a chemical reaction and they are different from the products which are the final substances after the reaction takes place.
Four drops of yellow food coloring are added to 10 mL of water. The mixture is pale yellow. Did a chemical or physical change take place?
Physical Change
According to the law of conservation of mass, what happens to the total mass of substances during a chemical reaction?
The total mass of substances remains constant (stays the same) during a chemical reaction.
Which of the following is a compound?
H
He
HF
HF
Hydrogen and Fluorine
Which of the following is an example of a chemical process?
* Cutting a piece of wood into small wood chips
* Burning a marshmallow
B. burning a marshmallow
A metal object rusts. Is this a physical or chemical change?
This is a chemical change because the metal reacts with oxygen to form a new substance which is the rust. Rust has different properties than both the metal and the oxygen.
Scientists sometimes use chemical reactions to reclaim metals from solutions to reduce toxic waste. Does this mean that the metal has disappeared?
No, it is not possible for materials to ever disappear (destroyed) completely.
Define an open system and how does it relate to conservation of mass?
Open system: Mass can enter or leave the system.
Exothermic and Endothermic Reactions:
An endothermic reaction will make the environment around it feel _______.
Hot/Cold
Cold
*absorbs energy*
Which of the following is true about chemical reactions?
*The total mass of the products is less than the total mass of the reactants.
*The total mass of the products is equal to the total mass of the reactants.
The total mass of the products is equal to the total mass of the reactants.
You crush an aluminum can. Is this a physical or chemical change?
This is a physical change because even though the substance changes form, it is still made of aluminum and has the same properties.
What is happening in chemical reactions at a molecular level?
Molecules are finding the most balanced state as possible
What is a closed system and how does it relate to conservation of mass?
No mass can enter or leave. Conservation of mass always holds true.
Are the atoms conserved in this reaction? Why or why not?
CH4 + 2O2 --> CO2 + 2H2O
Atoms are conserved. Their total number remains the same.
8. A reaction occurs between two liquids. Before the reaction, liquid A is clear and colorless. Liquid B is clear and light blue in color. When the two liquids are combined in a closed system, a cloudy, pale green solution is formed. Which of the following describes what has occurred?
* a physical reaction where mass was not conserved
* a chemical reaction where mass was conserved
What are the reactants and what are the products in this chemical equation?
CH4+2O2 --> CO2+2H2O
The reactants are methane and oxygen, and the products are carbon dioxide and water.
Are the molecules conserved in this reaction? Why or why not?
CH4 + 2O2 --> CO2 + 2H2O
Molecules are not conserved. New molecules are formed in the reaction.
20.A scoop of baking soda is added to vinegar in a beaker, producing a solution that fizzes and releases gas bubbles. The total mass of the substances, the beaker, and the measuring scoop were recorded before and after the baking soda was added to the beaker of vinegar. Did the reaction occur in an open or closed system?
The reaction occurred in an open-system