GCSE›AQA GCSE Chemistry›Mind mapsConservation of Mass and Balanced EquationsAQA GCSE Chemistry: Mind mapStudy pack PDFAlso for this subtopic:Revision notesFlashcardsSubtopic testCover factsThe lawNo atoms lost or made in a reactionMass of products = mass of reactantsAtoms are just rearrangedSo equations must be balancedBalancingChange only numbers in front of formulaeFront number multiplies the whole formulaSubscripts are fixed, never change themCHX4+2 OX2→COX2+2 HX2O\ce{CH4 + 2O2 -> CO2 + 2H2O}CHX4+2OX2COX2+2HX2O1 C, 4 H, 4 O on each sideApparent changeOpen system: gas escapes → mass decreasesCOX2\ce{CO2}COX2 lost from carbonate plus acid in open flaskGas joins from air → mass increasesBurning a metal gains oxygenMass Conservedbalanced equationsgmolClosed systemSealed: nothing enters or leavesNo mass change observedConfirms conservation of massFrom masses (HT)Convert each mass to molesFind simple whole number ratioRatio gives the balancing numbersExam tipsChanging HX2O\ce{H2O}HX2O to HX2OX2\ce{H2O2}HX2OX2 makes a different substanceExplain mass change by naming the gas