part 5. physical/chemical properties and changes -see daily review #3 in your notebook, too!
34. how is density calculated?
35. what is the density if the mass is 21 grams and the volume is 7.5 ml?
36. write pc for physical change and cc for chemical change:
_____ snow melting
_____ mud dries and changes to dust
_____ a match stick turns to ash while burning
_____ hydrogen and oxygen gas combining to become water
_____ teeth crushing food
_____ breaking a glass window with a baseball
_____ making salt by mixing sodium and chlorine together
37. is dissolving a pc or cc? __________ why?
38. what are the signs/evidence of a chemical change? (make a list)
39. in a chemical reaction, the atoms of the ______________ will ______________ to form the ______________. the properties of those new substances will be ______________ than the properties of the substances before the reaction occurred.
part 6. chemical reaction extras -see daily review #3 in your notebook, too!
40. what happens to temp in an endothermic reaction? __________ why?
41. what happens to temp in an exothermic reaction?__________ why?
42. how can changes in thermal energy be measured in the lab?
43. what is the law of conservation of matter?
a)how does it relate to mass?
b) how does it relate to the number of atoms?
43. how can changes in mass during a chemical reaction be measured in the lab?
44. how does an open container affect mass in a reaction?
45. how many molecules are in 2 so₄? __________how many molecules are in 3 n₂o?
-atoms of sulfur?__________ -atoms of nitrogen?__________
-atoms of oxygen?__________ -atoms of oxygen?__________
46. are the following equations balanced? write yes or no on the blank. draw pictures if needed.
2 naf + mgcl₂ → mgf₂ + 2 nacl __________
4 na + 4h₂o → 4 naoh + h₂ __________
3 h₂o₂ + → 3 h₂o + 2 o₂ __________

Question

part 5. physical/chemical properties and changes -see daily review #3 in your notebook, too!
34. how is density calculated?
35. what is the density if the mass is 21 grams and the volume is 7.5 ml?
36. write pc for physical change and cc for chemical change:
_____ snow melting
_____ mud dries and changes to dust
_____ a match stick turns to ash while burning
_____ hydrogen and oxygen gas combining to become water
_____ teeth crushing food
_____ breaking a glass window with a baseball
_____ making salt by mixing sodium and chlorine together
37. is dissolving a pc or cc? __________ why?
38. what are the signs/evidence of a chemical change? (make a list)
39. in a chemical reaction, the atoms of the ______________ will ______________ to form the ______________. the properties of those new substances will be ______________ than the properties of the substances before the reaction occurred.
part 6. chemical reaction extras -see daily review #3 in your notebook, too!
40. what happens to temp in an endothermic reaction? __________ why?
41. what happens to temp in an exothermic reaction?__________ why?
42. how can changes in thermal energy be measured in the lab?
43. what is the law of conservation of matter?
    a)how does it relate to mass?
    b) how does it relate to the number of atoms?
43. how can changes in mass during a chemical reaction be measured in the lab?
44. how does an open container affect mass in a reaction?
45. how many molecules are in 2 so₄? __________how many molecules are in 3 n₂o?
    -atoms of sulfur?__________             -atoms of nitrogen?__________
    -atoms of oxygen?__________             -atoms of oxygen?__________
46. are the following equations balanced? write yes or no on the blank. draw pictures if needed.
    2 naf + mgcl₂ → mgf₂ + 2 nacl  __________
    4 na + 4h₂o → 4 naoh + h₂  __________
    3 h₂o₂ + → 3 h₂o + 2 o₂  __________

Accepted Answer

### Question 34: How is density calculated?
# Explanation:
## Step1: Recall density formula
Density is defined as mass per unit volume. The formula is $
ho = \frac{m}{V} $, where $
ho $ (rho) is density, $ m $ is mass, and $ V $ is volume.
# Answer:
Density is calculated by dividing mass by volume, using the formula $
ho = \frac{m}{V} $ (or "Density = Mass / Volume").

### Question 35: What is the density if the mass is 21 grams and the volume is 7.5 mL?
# Explanation:
## Step1: Identify formula and values
Use $
ho = \frac{m}{V} $, where $ m = 21 \, \text{g} $, $ V = 7.5 \, \text{mL} $.
## Step2: Substitute and calculate
$
ho = \frac{21}{7.5} = 2.8 \, \text{g/mL} $.
# Answer:
The density is $ 2.8 \, \text{g/mL} $.

### Question 36: Classify changes as PC (physical) or CC (chemical)
- **Snow melting**: PC (state change, no new substance).
- **Mud dries and changes to dust**: PC (water evaporates, no new substance).
- **A match stick turns to ash while burning**: CC (combustion, new substances like ash).
- **Hydrogen and oxygen gas combining to become water**: CC (new substance H₂O formed).
- **Teeth crushing food**: PC (physical breakdown, no new substance).
- **Breaking a glass window with a baseball**: PC (physical breakage, no new substance).
- **Making salt by mixing sodium and chlorine together**: CC (new substance NaCl formed).

# Answer:
- Snow melting: PC
- Mud dries and changes to dust: PC
- A match stick turns to ash while burning: CC
- Hydrogen and oxygen gas combining to become water: CC
- Teeth crushing food: PC
- Breaking a glass window with a baseball: PC
- Making salt by mixing sodium and chlorine together: CC

### Question 37: Is dissolving a PC or CC? Why?
# Brief Explanations:
Dissolving is typically a physical change (PC) because it involves mixing a solute into a solvent (e.g., sugar in water) without forming a new substance (the sugar can be recovered by evaporation, and the chemical identity of the solute/solvent remains).
# Answer:
PC; because dissolving usually does not form a new substance (the solute can be separated, and chemical identities of solute/solvent remain).

### Question 38: Signs/evidence of a chemical change
# Brief Explanations:
Common signs of a chemical change include: formation of a precipitate (solid from solution), gas production (bubbling), color change, temperature change (energy absorbed/released), and formation of a new substance (e.g., rust, ash).
# Answer:
Signs of chemical change: precipitate formation, gas production, color change, temperature change, new substance formation.

### Question 39: Fill in the blanks about chemical reactions
In a chemical reaction, the atoms of the **reactants** will **rearrange** to form the **products**. The properties of those new substances will be **different** than the properties of the substances before the reaction occurred.
# Answer:
reactants; rearrange; products; different

### Question 40: What happens to temp in an endothermic reaction? Why?
# Brief Explanations:
In an endothermic reaction, temperature **decreases** (or the surroundings cool down) because the reaction absorbs thermal energy from the surroundings.
# Answer:
Temp decreases; because the reaction absorbs heat from the surroundings.

### Question 41: What happens to temp in an exothermic reaction? Why?
# Brief Explanations:
In an exothermic reaction, temperature **increases** (or the surroundings warm up) because the reaction releases thermal energy into the surroundings.
# Answer:
Temp increases; because the reaction releases heat into the surroundings.

### Question 42: How to measure thermal energy changes in lab?
# Brief Explanations:
Use a thermometer to measure temperature changes (e.g., in a calorimeter, monitor temp before/after reaction). Thermal energy change relates to temperature change (and mass/specific heat, via $ q = mc\Delta T $).
# Answer:
Measure temperature change with a thermometer (e.g., in a calorimeter) and use $ q = mc\Delta T $ (heat = mass × specific heat × temp change) to calculate thermal energy change.

### Question 43: Law of conservation of matter
- **Law**: Matter (mass) is neither created nor destroyed in a chemical reaction.
- **a) Relation to mass**: Mass is conserved (total mass of reactants = total mass of products).
- **b) Relation to number of atoms**: The number of each type of atom is conserved (atoms rearrange, not created/destroyed).
# Answer:
- Law: Matter is neither created nor destroyed in a chemical reaction.
- a) Mass is conserved (reactant mass = product mass).
- b) Number of each atom is conserved (atoms rearrange, not added/removed).

### Question 43 (second): How to measure mass changes in a chemical reaction?
# Brief Explanations:
Use a balance to measure mass of reactants before reaction and products after reaction (in a closed system to prevent mass loss/gain). Compare initial and final masses.
# Answer:
Measure mass of reactants (before) and products (after) with a balance (in a closed container to avoid mass loss/gain).

### Question 44: How does an open container affect mass in a reaction?
# Brief Explanations:
In an open container, gases can escape (e.g., CO₂ from a reaction) or enter (e.g., O₂). Thus, mass may appear to decrease (if gas escapes) or increase (if gas is absorbed), violating apparent mass conservation (but matter is still conserved overall).
# Answer:
In an open container, mass may change (decrease if gas escapes, increase if gas is absorbed) because matter (e.g., gas) can enter/leave the container.

### Question 45: Molecules and atoms in formulas
- For $ 2 \, \text{SO}_4 $:
  - Molecules: $ 2 $ (the coefficient is 2).
  - Atoms of sulfur: $ 2 \times 1 = 2 $ (each $ \text{SO}_4 $ has 1 S).
  - Atoms of oxygen: $ 2 \times 4 = 8 $ (each $ \text{SO}_4 $ has 4 O).

- For $ 3 \, \text{N}_2\text{O} $:
  - Molecules: $ 3 $ (coefficient is 3).
  - Atoms of nitrogen: $ 3 \times 2 = 6 $ (each $ \text{N}_2\text{O} $ has 2 N).
  - Atoms of oxygen: $ 3 \times 1 = 3 $ (each $ \text{N}_2\text{O} $ has 1 O).

# Answer:
- $ 2 \, \text{SO}_4 $:
  Molecules: $ 2 $; S atoms: $ 2 $; O atoms: $ 8 $
- $ 3 \, \text{N}_2\text{O} $:
  Molecules: $ 3 $; N atoms: $ 6 $; O atoms: $ 3 $

### Question 46: Are the equations balanced?
1. $ 2 \, \text{NaF} + \text{MgCl}_2
ightarrow \text{MgF}_2 + 2 \, \text{NaCl} $:
   - Na: 2 (left) = 2 (right)
   - F: 2 (left) = 2 (right)
   - Mg: 1 (left) = 1 (right)
   - Cl: 2 (left) = 2 (right)
   Balanced: Yes.

2. $ 4 \, \text{Na} + 4 \, \text{H}_2\text{O}
ightarrow 4 \, \text{NaOH} + \text{H}_2 $:
   - Na: 4 (left) = 4 (right)
   - H: $ 4 \times 2 = 8 $ (left) vs. $ (4 \times 1) + 2 = 6 $ (right) → Unbalanced.
   Balanced: No.

3. $ 3 \, \text{H}_2\text{O}_2
ightarrow 3 \, \text{H}_2\text{O} + 2 \, \text{O}_2 $:
   - H: $ 3 \times 2 = 6 $ (left) vs. $ 3 \times 2 = 6 $ (right)
   - O: $ 3 \times 2 = 6 $ (left) vs. $ (3 \times 1) + (2 \times 2) = 7 $ (right) → Unbalanced.
   Balanced: No.

# Answer:
- $ 2 \, \text{NaF} + \text{MgCl}_2
ightarrow \text{MgF}_2 + 2 \, \text{NaCl} $: Yes
- $ 4 \, \text{Na} + 4 \, \text{H}_2\text{O}
ightarrow 4 \, \text{NaOH} + \text{H}_2 $: No
- $ 3 \, \text{H}_2\text{O}_2
ightarrow 3 \, \text{H}_2\text{O} + 2 \, \text{O}_2 $: No

Sovi.AI - AI Math Tutor

QUESTION IMAGE

Question

Explanation:

Question 34: How is density calculated?

Step1: Recall density formula

Step1: Identify formula and values

Step2: Substitute and calculate

Answer:

Question 35: What is the density if the mass is 21 grams and the volume is 7.5 mL?