A chemical reaction happens when substances change to form new substances., , Reactants are the starting substances in a chemical reaction., , Products are the new substances formed during a reaction., , In a chemical change, new substances are made and the change is usually difficult to reverse., , A physical change does not create a new substance and is often reversible., , Atoms are the smallest particles that make up elements., , Molecules are formed when two or more atoms join together chemically., , A compound contains two or more different elements chemically bonded., , A mixture contains substances that are not chemically bonded., , Elements contain only one type of atom., , During combustion, a substance reacts quickly with oxygen and releases energy., , Oxidation happens when a substance gains oxygen., , Neutralisation occurs when an acid reacts with a base to form salt and water., , Acids have a pH lower than seven., , Alkalis are soluble bases with a pH higher than seven., , Indicators can be used to test whether a substance is acidic or alkaline., , Temperature change can be evidence that a chemical reaction has taken place., , A colour change can show that a new substance has formed., , Gas bubbles may form during a chemical reaction., , A precipitate is a solid formed from two solutions reacting., , Mass is conserved in a chemical reaction., , In a closed system, the total mass before and after a reaction stays the same., , Particles rearrange during a chemical reaction., , No atoms are created or destroyed in a chemical reaction., , Burning magnesium produces magnesium oxide., , When vinegar reacts with baking soda, carbon dioxide gas is produced., , Rusting is an example of oxidation., , Iron reacts with oxygen and water to form rust., , Energy changes occur during chemical reactions., , Exothermic reactions release energy to the surroundings., , Endothermic reactions take in energy from the surroundings., , Heating can speed up many chemical reactions., , Increasing the surface area of a solid can increase the rate of reaction., , Stirring can help reactants mix and react faster., , A catalyst speeds up a reaction without being used up., , Enzymes are biological catalysts., , The pH scale measures how acidic or alkaline a solution is., , Strong acids have very low pH values., , Strong alkalis have very high pH values., , Water is neutral and has a pH of seven., , Acids can react with metals to produce a salt and hydrogen gas., , Acids can react with carbonates to produce a salt, water and carbon dioxide., , Chemical equations show reactants turning into products., , Word equations use words to describe a reaction., , Symbol equations use chemical formulas to describe a reaction., , Balanced equations show equal numbers of each type of atom on both sides., , The arrow in a chemical equation means “reacts to form.”, , Some reactions are reversible., , In a reversible reaction, products can change back into reactants., , Understanding key terms helps explain and predict chemical reactions., .

Changing Substances

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