Energy Flow and Endo Exo.key
ENERGY FLOW Can you...? •Explain and diagram how energy flows. •Define system and surroundings. •Define endothermic and exothermic?
DIAGRAMMING ENERGY FLOW •
Energy flow is often drawn via diagram, with arrows showing where the energy is going.
•
For example, this diagram shows a burning piece of food. The energy is leaving the food and going into the can and the air, as shown by the arrows.
DIAGRAMMING ENERGY FLOW •
Here’s another example: this time the energy of a glass of water is going into the ice cube.
•
(It’s always “heat energy” that moves. There is no such thing as “cold energy.” Something that is cold just doesn’t have a lot of heat energy!)
SYSTEM & SURROUNDINGS •
When talking about energy, chemists & physicists identify two things: the system and the surroundings.
•
In a diagram, the system is usually circled. It is the part that we are focused on/paying attention to. There isn’t really a “correct” answer for what the system is. You’ll have to decide on it for each problem. In this example, we could say that the system is the ice cube. (So I’ve circled it.)
•
The surroundings are everything else in the whole world, including the water, the glass, etc.
•
So in this example, energy is leaving the surroundings and going in to the system. Note: Often, when people talk about “systems” they mean something with multiple parts. For example, a system of equations has more than one equation. Or a machine, with lots of parts working together, might be called a system. In chemistry, we use the word system differently. It is the one thing we’re focused on. It does not have to be multiple parts.
SYSTEM & SURROUNDINGS • This
time, I’ve circled the burning piece of food. So it’s the system.
• The
can, water in the can, air, etc. are all part of the surroundings.
• So
in this example, energy is leaving the system and going in to the surroundings.
SYSTEM & SURROUNDINGS • But... I
could define it differently, if I wanted to.
•I
could say that the can & water is the system. The burning food, air, etc. are all part of the surroundings.
• So
in this example, energy is leaving the surroundings and going in to the system.
ENDOTHERMIC & EXOTHERMIC • Exothermic: Something
is exothermic when energy is leaving (exiting = exothermic.)
• Endothermic: Something
is endothermic when energy is entering. (Enter = endothermic)
• In
the example on the right, it is endothermic for the ice cube, because energy is going in.
ENDOTHERMIC & EXOTHERMIC • In
this example, it is exothermic for the burning food, because energy is leaving.
ENDOTHERMIC & EXOTHERMIC • But, it
is endothermic for the can and water, because energy is entering the can!
• It’s
really important to define your system!
ENDOTHERMIC & EXOTHERMIC • What
about boiling water? Is it endothermic or exothermic for the water?
ENDOTHERMIC & EXOTHERMIC • What
about boiling water? Is it endothermic or exothermic for the water?
• It’s
endothermic for the water!
ENDOTHERMIC & EXOTHERMIC
• How
about water that’s freezing in to ice?
ENDOTHERMIC & EXOTHERMIC • How
about water that’s freezing in to ice?
• It’s
exothermic for the water. Energy has to leave so that the water can freeze into ice!
DIAGRAMMING ENERGY FLOW •
Energy flow is often drawn via diagram, with arrows showing where the energy is going.
•
For example, this diagram shows a burning piece of food. The energy is leaving the food and going into the can and the air, as shown by the arrows.
DIAGRAMMING ENERGY FLOW •
Here’s another example: this time the energy of a glass of water is going into the ice cube.
•
(It’s always “heat energy” that moves. There is no such thing as “cold energy.” Something that is cold just doesn’t have a lot of heat energy!)
SYSTEM & SURROUNDINGS •
When talking about energy, chemists & physicists identify two things: the system and the surroundings.
•
In a diagram, the system is usually circled. It is the part that we are focused on/paying attention to. There isn’t really a “correct” answer for what the system is. You’ll have to decide on it for each problem. In this example, we could say that the system is the ice cube. (So I’ve circled it.)
•
The surroundings are everything else in the whole world, including the water, the glass, etc.
•
So in this example, energy is leaving the surroundings and going in to the system. Note: Often, when people talk about “systems” they mean something with multiple parts. For example, a system of equations has more than one equation. Or a machine, with lots of parts working together, might be called a system. In chemistry, we use the word system differently. It is the one thing we’re focused on. It does not have to be multiple parts.
SYSTEM & SURROUNDINGS • This
time, I’ve circled the burning piece of food. So it’s the system.
• The
can, water in the can, air, etc. are all part of the surroundings.
• So
in this example, energy is leaving the system and going in to the surroundings.
SYSTEM & SURROUNDINGS • But... I
could define it differently, if I wanted to.
•I
could say that the can & water is the system. The burning food, air, etc. are all part of the surroundings.
• So
in this example, energy is leaving the surroundings and going in to the system.
ENDOTHERMIC & EXOTHERMIC • Exothermic: Something
is exothermic when energy is leaving (exiting = exothermic.)
• Endothermic: Something
is endothermic when energy is entering. (Enter = endothermic)
• In
the example on the right, it is endothermic for the ice cube, because energy is going in.
ENDOTHERMIC & EXOTHERMIC • In
this example, it is exothermic for the burning food, because energy is leaving.
ENDOTHERMIC & EXOTHERMIC • But, it
is endothermic for the can and water, because energy is entering the can!
• It’s
really important to define your system!
ENDOTHERMIC & EXOTHERMIC • What
about boiling water? Is it endothermic or exothermic for the water?
ENDOTHERMIC & EXOTHERMIC • What
about boiling water? Is it endothermic or exothermic for the water?
• It’s
endothermic for the water!
ENDOTHERMIC & EXOTHERMIC
• How
about water that’s freezing in to ice?
ENDOTHERMIC & EXOTHERMIC • How
about water that’s freezing in to ice?
• It’s
exothermic for the water. Energy has to leave so that the water can freeze into ice!
