Atoms and Molecules | Grade 8 Science DepEd MELC Quarter 3 Module 2

[Music] hi there in our previous lesson we talked about the properties of solids liquids and gases based on the particle nature of matter if you still haven't watched the previous lesson you can pause this video and watch that one first to better understand our lessen today let's get started matter undergoes either physical or chemical change physical change is a change in one or more physical properties of matter without changing its chemical properties examples of physical change include changes in the size or shape of matter like when you fold a piece of paper to origami art changes of state from solid to liquid or from liquid to gas are also examples of a physical change chemical change occurs when a substance is transformed into another substance like when you burn a piece of paper most substances can exist in three phases depending on a temperature and atmospheric pressure some substances like water can exist in all three phases at ordinary conditions when heat energy is absorbed also referred to as endothermic or released or exothermic from a system one phase can change to another change in the energy of a system can cause the particles to move faster or slower resulting in changes in the arrangement and attractive forces existing among molecules phase change is the process of changing from one physical state of matter to another phase changes are physical changes because it only affects physical appearance not chemical makeup like most substances water can exist in three distinct states namely solid liquid or gas for example when ice melts it undergoes a change from solid to liquid when water boils steam is formed and this signals a change of phase from liquid to gas at certain temperatures water changes from one state to another the water molecule contains two hydrogen atoms and one oxygen atom covalently bonded however there is no change in the composition of water the particles that make up ice water and steam will contain two atoms of hydrogen and one atom of oxygen a phase change is just one type of physical change temperature is related to molecular or atomic motion because when the heat increases it makes the molecules move faster and when the temperature decreases the motion also decreases in the atoms molecular motion determines which phase of matter is observed slow moving molecules may be found in solids while rapid moving molecules are present in gases liquids have molecules in motion that are slower than gases but much more rapid than those of a solid during a phase change heat energy is either absorbed or released heat energy is released as molecules slow down and move closer together heat energy is absorbed as molecules speed up and expand if pressure is constant the state of a substance will depend entirely on the temperature it is exposed to for this reason ice melts if taken out of a freezer and water boils out of a pot if left at too high a temperature for too long temperature is merely a measurement of the amount of heat energy present in the surroundings when a substance is placed in surroundings of a different temperature heat is exchanged between the substance and the surroundings causing both to achieve an equilibrium temperature this figure shows the melting and freezing of water as you can see water is still in its solid state and the water molecules are close to each other the water molecules move very slow the energy needed for a substance to change the state is latent heat as it absorbs latent heat the kinetic energy of water molecules increases so they vibrate and move faster at some point they have enough energy to overcome the forces that hold them in their fixed places so they break away from their fixed positions in the solid the arrangement of water molecules in ice gradually becomes disorganized and the ice turns to liquid water in this phenomenon as water absorbs heat from the surroundings the surroundings become cooler on the other hand when the liquid water releases its latent heat to the surroundings the water molecules start to slow down and they become closer to each other as they become closer to each other the attraction between molecules becomes stronger and start turning to solid water also known as ice this figure shows the change of liquid water to water vapor and vice versa in the same way when liquid water absorbs latent heat from the surroundings the water molecules start to move faster and at some point have enough energy to overcome the attraction between them as they overcome the bond between water molecules the molecules move faster and turn into gas or what we call water vapor in contrary when water releases the latent heat to the surroundings the gas molecules move slower causing them to become closer to each other creating more attraction between molecules and turning the gas into liquid water [Music] when an ice cube is exposed to heat its water molecules absorb heat energy from the surrounding atmosphere thus it is endothermic as the water molecules begin to move more energetically the solid ice cube melts into liquid water when an ice cube melts its shape changes and it acquires the ability to flow but its composition does not change melting is an example of a physical change though its physical properties change molecules stay the same the temperature at which ice melts is 0 degrees celsius freezing or solidification occurs when liquid water freezes into a solid state or ice and it appears to have changed water starts to freeze at zero degrees celsius and lower as heat is released from the water the molecules lose kinetic energy and the velocity of the molecules decreases freezing happens when a substance releases heat energy it is exothermic the particles are practically put together causing them to stop moving entirely have you noticed that ice cubes left in the freezer for a long time shrink it is because they sublime similarly moth walls when left for several days insider cabinets disappear without proof that it was converted to liquid the moth balls do not merely disappear but they have been converted to gas without passing the liquid state moth balls produce a strong odor because the molecules have escaped from the solid mothball into the air thus becoming gas molecules this change of state from solid to gas is called sublimation since the substance absorbs heat energy it is endothermic dry ice or solid carbon dioxide has a very high rate of sublimation when water vapor comes in contact with a cold glass window in winter it forms a solid deposit on the window glass called frost deposition is the process by which a substance changes from gas to a solid without first changing into the liquid phase deposition is the reverse of sublimation when water vapor high up in the air changes directly into solid ice crystals you get snowflakes heat energy is released as the crystals form thus it is exothermic observe a pot of water on a burner and allow it to boil when the water boils observe the bubbles in the container these bubbles contain water vapor or water in the form of a gas additional energy that is absorbed increases the energy in motion or kinetic energy of the liquid molecules it is endothermic particles that escape the liquid enter the gas phase this is an example of a liquid changing to a gaseous state the process is called evaporation the temperature in which water boils is 100 degrees celsius the reverse process of evaporation is called condensation the change from gaseous to liquid form occurs when warm water vapor in the air rises to cooler levels it condenses and forms into clusters of tiny water droplets called clouds molecules of gas move very fast and in random motion they possess high kinetic energy that can overcome any attractive forces holding them together however when the temperature is lowered the gas particles sufficiently slow down the intermolecular attractions increase overcoming the tendency to move apart since the substance releases heat energy it is exothermic consider the cycling of water in our environment because of the sun's heat water from the oceans and other bodies of water changes from a liquid to a gas this provides 90 percent of the moisture in our atmosphere most of the remaining 10 percent found in the atmosphere is released by plants in addition a very small portion of water vapor enters the atmosphere through the process by which water changes directly from solid ice or snow to a gas after water vapor enters the lower atmosphere rising air currents carry it upward where the air is cooler in the cool air water vapor is more likely to change from a gas into a liquid to form cloud droplets cloud droplets can grow and produce rain that falls over the land surface and the cycle continues now let's wrap things up matter exists in three phases solid liquid and gas matter undergoes changes in physical state known as phase changes the phase changes that absorb energy or endothermic are melting evaporation and sublimation while the phase changes that release energy or exothermic are condensation freezing and deposition there are six ways to change the phase of matter melting changes a solid to liquid freezing changes a liquid to solid evaporation turns liquid to gas on the surface of a liquid condensation transforms gas to liquid sublimation changes a solid to gas deposition changes a gas to solid that's all for now we will be discussing about the identity of a substance according to its atomic structure in our next video so stay tuned see you on our next video and don't forget to keep your minds busy if you like this video please subscribe to our channel and hit the notification icon for more videos like this

Channel: The Learning Bees

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Keywords: The Learning Bees, Department of Education, DepEd, MELC-Based, Most Essential Learning Competencies, Science, MELC, Grade 8, Phases of matter, phase change, physical change, chemical change, motion of molecules and atoms, exothermic, endothermic, boiling point, freezing point, melting point, melting, freezing, solidification, sublimation, deposition, how snowflakes form, frost, evaporation, condensation, water cycle, how clouds form, why is there rain, transpiration

Id: 9Pdo0-qkEIY

Length: 13min 14sec (794 seconds)

Published: Wed Apr 14 2021