👤 By the CinnaEntry Content Team🕐 Updated 2026-09-06🏷️ HESI Chemistry🔖 Free to read, print, and share
Also known as: reactants · products · balanced equation · catalyst · conservation of mass
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Use this one-page guide to lock in Reactions Cheat Sheet for the ATI TEAS 7 and HESI A2. Keep it handy during review and on exam day.
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📒 The 1-minute cheat sheet
📌 The Equation
Reactants (left) → products (right)
Balanced = same atoms of each element on BOTH sides
Change COEFFICIENTS in front, never subscripts inside
📌 Energy
EXOthermic — heat OUT, feels warm
ENDOthermic — heat IN, feels cold
📌 Catalyst
Speeds the reaction, is NOT used up
Enzymes are biological catalysts
📌 Chemical Or Physical?
Ask: is there a NEW substance?
New → chemical (rusting, burning, digesting)
No → physical (melting, dissolving, cutting)
📚 Reactions Cheat Sheet — full study notes
The cheat sheet above is your quick recall card. These notes go deeper — what it is, what to do first, what must be reported, and what to teach.
In a chemical reaction, atoms are rearranged into new substances but never created or destroyed. That single principle — conservation of mass — is what makes an equation need balancing, and it is the reasoning most reaction questions test.
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Key points
Understand these first
Reactants are on the LEFT of the arrow; products are on the RIGHT.
A balanced equation has the same number of each type of atom on both sides, because matter is conserved.
A CATALYST speeds a reaction and is NOT consumed by it. Enzymes are biological catalysts.
Exothermic reactions RELEASE heat; endothermic reactions ABSORB it.
A chemical change makes a new substance (rusting, burning); a physical change does not (melting, dissolving, cutting).
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Study first
Where to start
2H₂ + O₂ → 2H₂O: four hydrogen and two oxygen atoms on the left, and the same four and two on the right. Balanced.
An enzyme lets a reaction in the body run at body temperature that would otherwise need high heat — and the enzyme is still there afterwards, ready to act again.
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Red flags — report now
Escalate immediately
Changing a chemical formula (H₂O → H₂O₂) to balance an equation. You may only change the COEFFICIENTS in front.
Believing a catalyst is used up; if it were, it would be a reactant.
Calling dissolving or melting a chemical change — no new substance forms, so both are physical.
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Commonly tested
What comes up most
Count atoms element by element in a column under each side. Balancing becomes bookkeeping rather than guesswork.
To classify a change, ask one question: is there a NEW substance? If not, it is physical.
❓ Reactions Cheat Sheet: TEAS & HESI FAQs
What should I focus on first when studying Reactions Cheat Sheet?
2H₂ + O₂ → 2H₂O: four hydrogen and two oxygen atoms on the left, and the same four and two on the right. Balanced. An enzyme lets a reaction in the body run at body temperature that would otherwise need high heat — and the enzyme is still there afterwards, ready to act again.
What are the warning signs of Reactions Cheat Sheet a nurse must report?
Changing a chemical formula (H₂O → H₂O₂) to balance an equation. You may only change the COEFFICIENTS in front. Believing a catalyst is used up; if it were, it would be a reactant. Calling dissolving or melting a chemical change — no new substance forms, so both are physical.
What do I need to know about Reactions Cheat Sheet for the TEAS or HESI?
Reactants are on the LEFT of the arrow; products are on the RIGHT. A balanced equation has the same number of each type of atom on both sides, because matter is conserved. A CATALYST speeds a reaction and is NOT consumed by it. Enzymes are biological catalysts. Exothermic reactions RELEASE heat; endothermic reactions ABSORB it.
What are the most commonly tested points on Reactions Cheat Sheet?
Count atoms element by element in a column under each side. Balancing becomes bookkeeping rather than guesswork. To classify a change, ask one question: is there a NEW substance? If not, it is physical.
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Quick Tip
Reactants are on the LEFT of the arrow; products are on the RIGHT.