Science Notes: Heat, Exothermic and Endothermic Reactions Flashcards
Classify the following as exothermic or endothermic: A cold pack gets cold when activated, a campfire gives off heat and light, water freezes in a freezer, a plant grows using sunlight.
This is an endothermic reaction because ‘endothermic reactions absorb energy from their surroundings.’ A campfire gives off heat and light: This is an exothermic reaction because ‘exothermic reactions release energy to their surroundings.’ Water freezes in a freezer: This is an exothermic process because ‘freezing water releases energy to its surroundings.’ A plant grows using sunlight: This is an endothermic process because ‘photosynthesis, which requires sunlight, absorbs energy from the surroundings.’
What is the difference between heat and temperature?
‘Heat is the transfer of thermal energy between objects with different temperatures,’ while ‘temperature is a measure of the average kinetic energy of the particles in a substance.’ In other words, heat is energy in motion, while temperature measures how fast particles are moving.
How does heat transfer from one object to another?
Heat always moves from a warmer object to a cooler one. As stated, ‘heat transfer is the movement of thermal energy from a warmer object to a cooler object.’
Describe the three methods of heat transfer.
Conduction: ‘Heat transfer through direct contact.’ For example, when a hot pan touches your hand, heat is transferred directly to your skin.
Convection: ‘Heat transfer through the movement of fluids (liquids and gases).’ For instance, warm air rises while cooler air sinks, creating convection currents.
Radiation: ‘Heat transfer through electromagnetic waves.’ An example is feeling the warmth of the sun on your skin without any direct contact.
How is thermal energy related to temperature?
‘Thermal energy is the total kinetic energy of all the particles in a substance.’ As temperature increases, ‘the average kinetic energy of particles increases,’ which means the thermal energy also increases. Essentially, higher temperature means higher thermal energy.
Which state of matter (solid, liquid, or gas) has the highest thermal energy? Why?
Gases have the highest thermal energy. This is because ‘gases have particles that are widely spaced and move rapidly in random directions.’ Adding heat to a gas ‘further increases the speed and motion of its particles,’ which means it has more thermal energy compared to solids or liquids.
