what is it mean change in state and separating endothermic and exothermic?
930214
solid to gas is endothermic reaction as it absorbs energy\ngas to solid is exothermic as it give off energy
327565
Because there is no temperature change. Temperature is a physical measurement of the phenomena of heat transfer to and from a system, not of redistribution of energy within a closed system. The process you describe occurs within the closed system, and cannot be recorded as a release of heat energy from the system or intake of heat energy into the system.
945938
endothermic because it takes in heat.
395234
if you go from A to be and then B to A you should have no overall energy change. one will be an exothermic reacion and the other should be endothermic reaction
211421
It's in the second law of thermodynamics. It's the measurement of disorder in the universe. Every time a chemical or physical reaction happens, it increases the entrophy (disorder) in the universe.
920392
it is exothermic, meaning the combustion reaction releases energy in the form of heat
141723
Temperature is the degree of heat and heat is the transfer of energy from one body to another as a result of a difference in temperature or a change in phase.
316710
well energy is used only in the beginning to start the reaction. otherwise an exothermic reaction will give out tremendous amount of heat energy.
776432
I am a HVAC trainer in the USA, and as such I have to explain the difference between energy (heat is a form of energy) and temperature. For the most part, my students do not posses any college background, and so I do my best to explain this in layman terms. There are chapters written on this subject, and to do it justice here …. well here goes.\n\nHeat is a form of energy, as is electricity, natural & propane gas, coil, gasoline, etc. Temperature is a measurement of how densely heat energy is packed into a substance. The more heat energy there is in a substance, the more vigorous the atoms and molecules will move. If the motion is vigorous enough, the substance can change its state and assume new characteristics (ice is different from liquid water, which is different from steam). \n\nThe temperature of a given amount of substance will increase as heat energy is added to that substance, and temperature will decrease as heat energy is taken (provided the substance does not change state). If a substance is at a temperature where it will change state, examples: ice~water @ 32deg F., …. and water~steam @ 212deg F. (at one atmosphere pressure), than the addition or subtraction of heat energy will cause the substance to change state, and the temperature will not change until the substance has finished changing state  “Sensible heat” is a form of energy that causes a change in temperature, “latent heat” energy causes a change in state.\n\n”Specific heat value” is the amount of heat energy it takes to rise or lower the temperature of one pound of a substance one degree F.  For instance, if we take one pound of ice at 0deg F., and put 1/2 BTU into that pound of ice, the temperature of that pound of ice will go up one degree F, thus .5 is the specific heat value of ice. If we continue to put energy into that ice, the temperature will go up one degree F. for every 1/2 BTU of energy we put in until it reaches 32deg F., at which time the ice will be at a temperature where it will melt if additional energy is put into it. We will have to put an additional 144 BTU’s to that one pound of ice at 32deg F., to change it into liquid water at 32deg F. \n\nOnce we have liquid water, we will have to put 1 BTU into that pound of water to raise the temperature 1deg F., thus 1.00 is the specific heat value of liquid water (please note: the specific heat value of liquid water changes slightly as the water’s temperature changes, but for most calculations, the constant “1.00” can be used). \n\nWhen the water reaches 212deg F. at one atmosphere (pressure at sea level), the water will once again be at a temperature where it can change state. As heat energy is added the liquid water, it will turn into steam. The amount of heat needed to change one pound of liquid water at 212deg F. into one pound of steam at 212deg F. is ….. ready ….. here it comes ….. 970 BTU’s …. That deserves a “wow”. \n\nThe reason I made such a big deal out of the 970 BTU’s is because it’s important that HVAC technicians and mechanics understand the concept that it takes a lot more energy to change the state of a substance than it does to change the temperature one degree Fahrenheit (or for that matter, one degree Celsius).
794929
Fire is an exothermic reaction because it releases energy.\nIf the temperature increases, it's because the heat is getting out of the molecule and therefore the reaction releases energy: which means it is exothermic.
255271
Yes you are correct.Different substances are different because of  their molecular structure and the constituents of each molecule. Molecules are well bound together in solids than in fluids (gases and liquids). The molecules are free in gases.\n Further the molecules are not at rest and are in vibrations.When the substance is heated  the average energy of a molecule  increases which tend to decrease the bindings of the molecules.\nGenerally by heating , a substance  chnges from solid to liquid and then to gaseous state.We call this as physical change.\nWhen the energy is  strong enough to break the  molecules into its constituent elements new compounds are produced we call it as chemical change.\nIn effect heat  has many things to do with their bondings
763107
Reactions can be classified as either exothermic or endothermic.  Exothermic reactions release energy, and cause the surroundings to increase in temperature.  Endothermic reactions absorb energy, and cause the temperature of the surroundings to decrease.
913643
Ectothermic means the animal is dependent on the outside environment for heat.\n\nHeterothermic means the animal's body temp. fluctuates as opposed to the constant temp. of a homeotherm.\n\nPoikilothermy - This refers to creatures whose internal temperatures vary, often matching the ambient temperature of the immediate environment
546552
It is called latent heat or the amount of heat required to change phases.  The latent heat of vaporization is usually much great than that of freezing.\n\nEach chemical or molecule has a different latent heat to change from liquid to gas.  It is also interesting that when water vapor condenses into liquid water, it gives off the exact same amount of energy that it took to boil it.\n\nNow think of dry ice (frozen carbon dioxide).  It goes straight from solid to gas (sublimation) and think about how much of a kick (freezing power) it has.
893091
Entropy (S) is the measure of disorder in a system. When thinking of problems such as this, it's helpful to think of it in terms of a gas being the highest entropy state, a liquid being kind of in the middle, and then a solid being the lowest entropy state.  \nA) A gas goes to another gas.  There should be no change in S.\nB) S is negative.  A gas condenses to a solid. You are moving from a higher state of entropy to a lower state.\nC) Positive S value. You go from the lowest energy state (solid) to an aqueous solution (liquid), which means the entropy goes up as well.
59109
The guy above me doesn't know what he's talking about.  He's confused.  \nThink about it: \nto freeze water, you need to take energy away from the water, right?  (You lower the temperature, which is the same thing as taking energy away.  Imagine sucking energy away from water to make it freeze.)  So, by definition, freezing water is exothermic.  It gives off energy.  Conversely, the melting of water is endothermic; you need to give ice energy in order for it to melt.  \nI know it can get confusing because when you touch ice, it's cold, so you might think that freezing is endothermic, but it's not.  If you think about it, ice in your hand is taking away energy from your hand in order for it to melt (that's why it feels cold), so melting is endothermic, making freezing exothermic.
726857
In thermodynamics, a state function, or state quantity, is a property of a system that depends only on the current state of the system, not on the way in which the system got to that state. \n\nA state function describes the equilibrium state of a system. \n\nFor example, internal energy, enthalpy and entropy are state quantities because they describe quantitatively an equilibrium state of thermodynamic systems. \n\nAt the same time, mechanical work and heat are process quantities because they describe quantitatively the transition between equilibrium states of thermodynamic systems.