PERIODIC TABLE
what does the atomic number of an element represent?
the number of protons in an atom
what is a chemical reaction?
when existing substances are converted into new substances
what does an exothermic reaction do to the surroundings?
releases heat, making them feel hotter
in a chemical equation, which side are the reactants on?
the left side
you mix two things and see bubbles. is this always a chemical reaction?
no - it could be a physical change like boiling
what is the vertical column in the period table called?
a group
name on indicator that a chemical reaction has occurred.
colour change
gas
precipitate
temperature change
sound/light
is photosynthesis endothermic or exothermic?
endothermic
write the word equation: magnesium reacts with oxygen to produce magnesium oxide
magnesium + oxygen -> magnesium oxide
you leave a glass of water in the sun and it evaporates. did a chemical reaction occur?
no - it's a physical change, not a chemical one
what do all elements in group 18 have in common?
they are noble gases and do not react easily
true or false: a chemical reaction always happens when two substances are mixed.
false
describe what happens to energy when a bond forms.
energy is released
what must be true for a chemical equation to be balanced?
the number and type of atoms must be the same on both sides
two substances are mixed. the temperature rises. is the reaction exothermic or endothermic?
exothermic - energy was released as heat
what's the difference between atomic mass and atomic number?
atomic mass = protons + neutrons
atomic number = protons only
what are the substances called that are used up in a reaction?
reactants
what happens to temperature during an endothermic reaction?
it decreases - the reaction absorbs heat
what type of equation uses chemical symbols instead of words?
a symbol equation
the chemical reaction is unbalanced. can it still be used to explain conservation of mass?
no - to follow the law, the equation must be balanced
why do group 17 elements (halogens) react similarly?
they have the same number of electrons in their outer shell
a yellow solid forms when two clear liquids are mixed. what is this solid called and what does it indicate?
a precipitate; it shows a chemical reaction occurred
explain how bond energy helps determine if a reaction is exothermic or endothermic
if more energy is used to break bonds than to form them, it's endothermic; if more is released forming bonds, it's exothermic
explain why balancing equations is important in relation to the conservation of mass.
it ensures that atoms are neither created nor destroyed - total mass stays the same
a student says atoms "disappear" during reactions. explain the mistake.
atoms are not destroyed; they are rearranged. mass is conserved.