please answer !! what is a precipitate ? + whats the differences between endothermic and exothermic reactions?
963889
A precipitate is a solid formed by a reaction. If you mix two chemicals in a test tube and a solid forms it is a precipitate.\n\nendothermic reactions absorb heat and will feel cold to the touch. Exothermic reactions give off heat and will feel warm or hot to the touch.
248591
CaO + H2O => Ca(OH)2\n\ncalcium oxide + water => calcium hydroxide\n\nThis is a great site for this - the reaction between CaO and water is an exothermic reaction (1)\n\nthe second reference is even better - not simply a diagram but a torn apart "self-heating" can\n\ngood luck!\n\nSomething else you might want to looking - MRE's (meals ready to eat)
82368
U get precipitate of Lead Iodide. The reaction is already mentioned!!!!\n\nPb(NO3)2 (aq) + 2KI (aq) --> 2KNO3 (aq) + PbI2 (s)
446541
An acid and a base react to form a salt and water.  For example:  NaOH + HCl ==> NaCl + H20.  The products will always include some sort of salt, as well as water, and the reation will always be exothermic, meaning energy is released.
462388
A reaction which gives out heat is known as 'exothermic'.\n\nhttp://en.wikipedia.org/wiki/Exothermic\nhttp://en.wikipedia.org/wiki/Exothermic_reaction\n\nA reaction which seems to absorb heat is known as 'Endothermic'\n\nhttp://en.wikipedia.org/wiki/Endothermic\nhttp://en.wikipedia.org/wiki/Endothermic_reaction
908972
Any combustion reaction is exothermic.\nSo a and b are exothermic.\nc is the dissociation of water, which involves breaking bonds, so it is endothermic.\nI think d is supposed to represent the melting of ice, which again takes in heat.
829949
energy input: reaction requires energy to take place - endothermic\nenergy output: reaction gives off energy when it takes place - exothermic
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i.e. it is easier to go backwards than forwards, so the product has more energy ( i.e. higher up the energy scale / nearer the top/ easier to get to the transition state ).\n\nHeat of reaction = heats of formation of products - reactants = 85 - 80 = +5kJ mol.... endothermic ( makes sense if products contain more energy than reactants )
869943
You could dissolve the crystal compound in water and measure the temperature change and specify whether there is an endothermic or exothermic change.  \n\nYou will need a thermometer.  Be careful as some crystal compounds are violently exothermic when dissolved in water.\n\nAndy
444820
Spontaneous combustion, or roughly, any spontaneous reaction would occur if the reactants are;\n1) thermodynamically unstable\n2) kinetically unstable\n\n1) Thermodynamic stability:\nAll combustion reactions are exothermic. If you draw the energy profile for a combustion reaction, the reactants are at a higher energy state and the products are at a lower energy state, since heat energy is released. Thermodynamic stability has to do with the relative energy of the reactants or products. As stated above, the reactants are at a higher energy state and they tend to release energy when reacting, so the reactants are said to be thermodynamically unstable. This unstability would result in a spontaneous reaction.\n\n2) Kinetic stability:\nThis takes into account the activation energy of the reaction. According to the 'Collision Theory', reacting molecules must have sufficient kinetic energy while colliding in order to overcome the activation energy for the proceeding reaction. Considering the thermodynamically unstable reactants above, if the reacting molecules can collide with each other with enough internal energy that is greater than or equal to the activation energy, they would be able to reach the transition state and form products spontaneously, and hence be termed kinetically unstable. \n\nIt happens, however, that in some combustion reactions, the reactants are thermodynamically unstable and you expect them to react just like that, but they don't because they're kinetically stable (internal energy not enough to overcome activation energy), and so they need to be given more internal energy in the form of a spark, ignition, presence of light etc., in order for the reaction to proceed.
372088
exothermic is the release of heat to the surroundings. endothermic is the absorption of heat from the surroundings.  Your temperature went up...think about it.  Part 2) specific heat of water is 4.18 j/gK, you have 55g substance. and temperature change was 9.7K...do the math.\nPart 3) well you have qH2O...it is the negative of deltaH!!\nPart 4) you have half as much NaOH...Half as much deltaH\nPart 5) divide delta H from part 3 by the number of moles NaOH in 2g NaOH
557678
Ah ha.  Thermite.  Magnesium ribbon would be the usual method to start this reaction.\n\nBe careful with this reaction...
732503
U CAN MAKE A PROJ ON REACTIONS ON THE FOLLOWING PTS  .\n INTRO OF REACTIONS\nDEFINITION OF A REACTION\n TYPES OF REACTIONS\n THEN, DESCRIBE THEM SEPARATELY
91636
Based on one of my chem classes:\n\nA reaction goes to completion if:\n>there's a precipitate.\n>one of the product is a gas and the system isn't isolated.\n>conditions are kept constant.\n\nI think the 'precipitation' you are asking is a 'precipitation reaction'. This effect is useful in many industrial and scientific applications whereby a chemical reaction may produce a solid that can be collected from the solution by various methods (e.g. filtration, decanting, centrifuging). Precipitation from a solid solution is also a useful way to strengthen alloys.
20960
Many chemical reactions release energy in the form of heat, light, or sound. These are exothermic reactions. Exothermic reactions may occur spontaneously and result in higher randomness or entropy (ÄS > 0) of the system. They are denoted by a negative heat flow (heat is lost to the surroundings) and decrease in enthalpy (ÄH < 0). In the lab, exothermic reactions produce heat or may even be explosive. \nThere are other chemical reactions that must absorb energy in order to proceed. These are endothermic reactions. Endothermic reactions cannot occur spontaneously. Work must be done in order to get these reactions to occur. When endothermic reactions absorb energy, a temperature drop is measured during the reaction. Endothermic reactions are characterized by positive heat flow (into the reaction) and an increase in enthalpy (+ÄH). \n\nExamples of Endothermic and Exothermic Processes \n\nPhotosynthesis is an example of an endothermic chemical reaction. \nIn this process, plants use the energy from the sun to convert carbon dioxide and water into glucose and oxygen. This reaction requires 15MJ of energy (sunlight) for every kilogram of glucose that is produced: \nsunlight + 6CO2(g) + H2O(l) = C6H12O6(aq) + 6O2(g) \n\nAn example of an exothermic reaction is the mixture of sodium and chlorine to yield table salt. This reaction produces 411 kJ of energy for each mole of salt that is produced:\n\nNa(s) + 0.5Cl2(s) = NaCl(s) \n\nEndothermic reactions take in energy from their surroundings\n\nDissolution of salt is endothermic because it takes energy from its surroundings not much but some.\n\nAs far as all salt types that is hard to say and you would have to do an experiment to find that out.
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No precipitate is formed.\nYou will see bubbles of carbon dioxide if there is enough HCI (Na2CO3+2HCI=2NaCI+H2O+CO2). If there isn't enough HCI ,Na2CO3+HCI=NaHCO3+NaCI happens ,you will see nothing.
290614
chemical reaction\n\nall substance give off some heat during change\n\nlook up kinetics on the web