Physical and Chemical Changes

Key Questions

• What is a chemical change?

  A chemical change is any change that results in the formation of new chemical substances with new properties.

  For example, hydrogen reacts with oxygen to form water. This is a chemical change.

  2H₂ + O₂ → H₂O

  Hydrogen and oxygen are both colourless gases, but water is a liquid at ordinary temperatures.

  EXAMPLES

  Which of the following are chemical changes? (a) Sugar dissolves in warm water. (b) A nail rusts. (c) A glass breaks. (d) A piece of paper burns. (e) Iron and sulfur form a shiny nonmagnetic grey substance on heating.

  Solutions:

  (a) Not a chemical change. The sugar and water are still present.
  (b) A chemical change. The reddish-brown rust is different from the iron.
  (c) Not a chemical change. The glass is just in smaller pieces.
  (d) A chemical change. The paper disappears. All that remains is a small amount of ash.
  (e) A chemical change. Sulfur is yellow, and iron is magnetic. The product is neither yellow nor magnetic.

  Here is video of a lab with a number of examples of both chemical and physical changes.
  
  video from: Noel Pauller

  Ernest Z. · 9 · Mar 28 2014
• How are physical changes different from chemical changes?

  Physical changes don't destroy your sample or make it into something new.

  Physical changes change the shape, size or phase of a substance. Crumpling paper, getting a haircut, dissolving salt in water, melting wax, making ice cubes, chopping veggies for tossed salad, growing crystals from a supersaturated solution, grinding metal and slicing bread are all physical changes.

  During a physical change the elements and compounds stay as they are.

  Chemical changes make new substances. Cooking an egg rearranges it's proteins. Burning fuels, etching metal with an acid, fermentation, respiration in your cells, decomposition in the compost pile, making zinc iodide in the lab, and forming a silver mirror are all chemical changes.

  During a chemical change the elements and compounds get rearranged and recombined into something new.

  Corinne F. · 9 · Mar 22 2014
• What is a physical change?

  Answer:

  A change in (matter or substance) which does not alter the chemical properties of the matter.

  Explanation:

  A physical change is a type of change in which the form of matter (substance) is altered but one substance is not transformed into another different substance. For example, if we carve a piece of wood into a baseball bat, it will still burn in a fire and float on water. It remains wood, so it is a physical change.

  (b) Crushing a can : after crushing can changes its shape, size but it still remain Aluminum so it is a physical change.

  Burning of wood is a chemical change because on burning wood changes to a totally different new products (ash, smoke and carbon dioxide).

  Here is video of a lab with a number of examples of both chemical and physical changes.
  
  video from: Noel Pauller

  Simple explanation with good results can be on this site http://chemistry.about.com/od/matter/a/10-Physical-Change-Examples.htm

  Manish Bhardwaj · 10 · Mar 23 2014

• How can you increase the speed of a chemical change?
• What is a chemical change?
• How are physical changes different from chemical changes?
• Do chemical changes involve energy?
• What is a physical change?
• Are physical changes reversible?
• Question #d9d76
• Is the protonolysis reaction of sulfuric acid in aqueous solution an example of chemical change?
• Question #76744
• What are the chemical changes of smores?
• What are the signs of a chemical change?
• Is milk souring a physical or chemical change?
• Question #5fe4a
• Is combustion a physical or chemical change? Why?
• Can a chemical change alter the total number of atoms?
• A light green powder is heated in a test tube. A gas is given off, and the solid becomes black. Was the change physical or chemical, and is the green powder an element, a compound, or a mixture?
• Question #72caa
• What might happen to a heated beaker made from glass that does not contain boron if the beaker were placed in a pan of ice water?
• What chemical change did the Statue of Liberty likely undergo?
• Do atoms/molecules change their arrangement during a physical change?
• Why is breaking down a compound into its elements considered a chemical change?
• Question #39e19
• Question #47ae6
• What is the chemical formula of sulphuric acid?
• If a box of crayons is left in a hot car on a summer afternoon, what change would you expect to observe in the crayons?
• Question #4ed7e
• Why is the rusting of an iron pole not a physical change?
• Question #d38ee
• A color change happens during an experiment mixing two liquids. Is this a physical change or chemical change?
• What is the component which dissolves in a solution called?
• Is a piece of copper cut in half a physical or chemical change?
• Is salt dissolving in water physical or chemical change?
• Is the freezing of mercury a reversible or irreversible physical change?
• Why are new properties observed during a change of state not signs of a chemical change?
• What is an example of a chemical change?
• In an experiment, a colour change is observed, and also observed is prolonged bubbling. Is this a chemical change?
• What name is given to substances that resist changes in pH?
• A firefly emits light. Is this a physical change?
• Is water boiling at 100 degrees Celsius a physical change?
• Is boiling water a physical or chemical change?
• Is cooking an egg an example of a physical or chemical change?
• Milk turns sour. Is this a chemical or physical change?
• Salt dissolves in water. Is this a chemical or physical change?
• Water boils. Is this a chemical or physical change?
• What are four possible clues that a a chemical change has taken place?
• How does a chemical change affect the composition of matter?
• What occurs when calcium chloride is reacted with sodium bisulfate?
• How did adding salt to ice change its freezing point?
• Why does an egg change color and texture when heated?
• Which property of physical changes explains why matter is conserved in a physical change?
• How can we tell if a chemical change has taken place?
• Is it correct to say that dissolving i a packet of juice powder in water makes a new substance, fruit punch, and so it must not be a physical change?
• Why is making play dough a physical change?
• Is distillation a physical change?
• Is evaporation a physical change?
• Is corrosion a physical change?
• Is sublimation a physical change?
• Is sublimation a chemical change?
• Is corrosion a chemical change?
• Is distillation a chemical change?
• Is evaporation a chemical change?
• Is evaporation a chemical or physical change?
• Is distillation a chemical or physical change?
• Is corrosion a chemical or physical change?
• Is sublimation a chemical or physical change?
• What are 3 examples of a chemical change?
• Is tarnishing (blackening) of silver a useful or harmful chemical change? Why?
• Is the production of heat or light evidence that a chemical change may have occurred?
• Is color change evidence that a chemical or physical change may have occurred?
• Is hammering a physical change?
• Is rotting wood a chemical or physical change?
• Is iron rust an example of a physical or chemical change?
• When sodium hydroxide dissolves in water is it a chemical or physical change?
• Is boiling point considered a physical or chemical change?
• Is a reaction with a base to form water physical or chemical change?
• Are reactions with water to form a gas physical or chemical changes?
• Is melting point considered a physical or chemical change?
• Would the reaction between dihydrogen and sodium hydroxide to give sodium and water be considered a chemical change?
• You go on vacation for a week and leave a bowl of fruit on the table. When you return you observe the pieces of fruit. What clues would indicate that the fruir has undergone a chemical change?
• Is making glue an example ot a chemical change or a physical change? How do you know?
• Question #9ab33
• What is changed when matter undergoes a physical change?
• What are examples of physical changes? Chemical changes?
• Is chemical change irreversible?
• Is tarnishing considered a physical or chemical change?
• Is burning considered a physical or chemical change?
• It is said chemical and physical properties are closely linked. Why does a chemical change also cause a change in physical properties?
• What speeds up chemical changes?
• Is dissolution a chemical change?
• Question #e57dc
• What characterizes chemical change?
• Question #98920
• How might you tell whether or not your toothpaste contained calcium carbonate, #CaCO_3#, or perhaps baking soda, #NaHCO_3#, without looking at the ingredients label?
• Is the explosion of fireworks a physical or chemical change?
• Michael mixes two chemicals together in a beaker. The chemicals change color, and the beaker heats up quickly. What kind of change most likely occurred?
• Is a bread being baked a physical or chemical change?
• Why are chemical changes different from physical changes?
• Is bubbling the sign of a chemical or physical change?
• What kind of changes (chemical or physical) do chefs use make to food?
• Is melting crayons is an example of a chemical or physical change?
• What are 5 examples of chemical changes?
• What is the differences between physical changes and chemical changes?
• Is adding sugar to lemonade a physical or chemical change?
• Is removing salt from water by evaporation considered a physical or chemical change?
• What are chemical changes and physical changes?
• What are the changes that occur inside a helium balloon as it rises from sea level?
• What are the five "clues" that a chemical change has occurred?
• Rusting metal is an example of what type of change?
• How can you tell that a hamburger is undergoing a chemical change when you cook it?
• What physical changes happen to water as it freezes?
• Question #cf954
• Question #b6df9
• Question #7e2d2
• Question #9747b
• Question #c40b2
• Is hydrogen and oxygen gas combining to form #H_2O# a chemical or physical change?
• When methanol is burned and leaves a residue is this a chemical or pyhsical change?
• An aspirin is crushed into fine power. Is this a physical or chemical change?
• Is baking cookies a physical or chemical change?
• Is cutting hair a physical or chemical change?
• Question #87413
• How is #"chemical change"# differentiated from #"physical change"#?
• What doesn't change during a physical change?
• The dissolving of which salt will produce both a physical and chemical change?
• Question #7b398
• When charcoal burns, it undergocs a chemical change that produces heat and light. Besides the charcoal, what is the other reactant in this chemical change?
• Question #862cc
• Is melting sugar a physical or chemical change?
• Rust is an example of what type of change?
• Question #ccc1e
• Question #1fa63
• Question #a18cd
• Does a lit candle provide an example of chemical change?
• Is deposition a physical or chemical change?
• Is condensation a physical or chemical change?
• Is evaporation a physical or chemical change?
• Question #2d4b8
• Is wood burning a physical or chemical change?
• What kind of reaction is represented by #2K + I_2 -> 2KI#?
• Question #3749a
• Question #ed5e2
• Question #2d155
• What term can be used to label the chemical change sodium cation undergoes after dissolving in water?
• #NH_4OH + HCl(aq) = NH_4Cl(aq) + H_2O(l)# no significant change can be noticed How to make sure that a reaction is really taking place ?
• Explain that magnetization of an iron nail is a physical change?
• Grapes hanging on the plant do not ferment but after being plucked from the plant can be fermented. Under what conditions do these grapes ferment? Is it a chemical or a physical?
• Question #f6876
• When baking soda is added to vinegar, it reacts vigorously, causing some fizzing and gas evolution. If a lit match is brought near the reaction flask, it is extinguished. What two key information help you identify this as a chemical change?
• The mass of a beaker containing a sample of water at 20°C was 109.44 g. After heating the sample to 60°C, the combined mass of the beaker and water was 109.08 g. Do these results contradict the law of conservation of mass?
• Question #68599
• Does freezing a substance change it?
• Why might a physical change require energy?