4-1 Observing Chemical Change
Which of the following is a chemical change in matter? Explain
a. bending a straw
b. boiling water
c. braiding hair
d. burning wood
Burning wood is a chemical change, because burning the wood changes it from wood into another substance, in this case carbon dioxide, water, and smoke
Define a closed system
Closed system - a place system where matter does not enter or leave. A sealed, airtight container is a closed system because matter does not enter or leave. Scientists can use closed systems to show the conservation of mass because nothing is entering or leaving it.
In general, what happens when you increase the temperature of a reaction?
The rate of the reaction increases.
Describe an exothermic reaction.
Exothermic reaction- a reaction where energy is released as chemical bonds in the reactants are broken. The energy is usually released as heat or light (think fire)
In an open system, such as a campfire, matter can _______
In an open system, such as a campfire, matter can enter from the surroundings or escape to the surroundings.
Define activation energy
Activation energy - the minimum amount of energy needed to start a chemical reaction. All chemical reactions need a certain amount of activation energy to get started (We need a spark to light a fire)
Describe and endothermic reaction.
Endothermic reaction- a reaction where extra energy is required to break the chemical bonds of the reactants. It often absorbs this energy from nearby matter, which can make the surroundings colder (think refrigerators)
What does the law of conservation of mass state?
Law of conservation of mass - during a chemical reaction, matter is not created or destroyed. All of the atoms present at the start of the reaction are present at the end of the reaction.
In an exothermic reaction, do the reactants have more energy than the products? Explain
Yes, the reactants have more energy than the products. Because an exothermic reaction releases the energy stored in chemical bonds of the reactants into the environment.
What are the three changes in physical properties that tell us that a chemical change occurred?
1. Formation of a precipitate- a solid that forms when two liquids chemically react (Chunks in spoiled milk)
2. Gas Production - often seen as bubbles (The bad smell in spoiled milk)
3. Color change - think cooking food, or an avocado turning brown (Spoiled milk turning from white to yellow)
Balance the chemical equation:
__P4 + __O2 ---> P4O6
1P4 + 3O2 ---> P4O6
In an endothermic reaction, do the reactants have more energy than the products? Explain
No, the product has more energy than the reactants. Because an endothermic reaction absorbs energy from the environment and stores it int he chemical bonds of the product.
You are on Zoom with your homie who is also learning about chemistry. She claims that the change from liquid water to water vapor is a chemical change. Tell them whether they are right or wrong and explain why.
When matter changes form, like from liquid water boiling turning into water vapor, it is a physical change. This is because physical changes are when a substance changes its form in some way, but it does not turn into a different substance. It is still water when it is a liquid and when it is a gas.
Balance the chemical equation:
CH4 + H2O ---> __CO + __H2
CH4 + H2O ---> 1CO + 3H2
List the four factors that can affect the rates of chemical reaction.
1. Surface Area - the more surface area there is on the reactants, the faster the reaction will be.
2. Temperature - increasing temperature speeds up reactions, decreasing temperature slows down reactions.
3. Concentration - the more of a substance that there is in an area, the faster a reaction happens
4. Catalysts and inhibitors - catalysts increase reaction rate by lowering activation energy needed, and inhibitors decrease reaction rate by increasing the increasing activation energy.