1. Size/usability
1.1. Must fit in pocket/hand, i.e. dont use 1l of water
1.2. Must be portable
1.3. If size is not small, it will be difficult to use, store, and take places where it may be required
2. Potential types of salts to use
2.1. Non-reusable Heat Packs
2.1.1. Magnesium Sulfate (MgSO₄)
2.1.2. Calcium Chloride (CaCl2)
2.1.3. Magnesium Chloride (MgCl₂)
2.1.4. Iron Powder (Fe)
2.2. Reusable Heat Packs
2.2.1. Sodium Acetate (CH₃COONa)
2.2.2. (Reheatable packs better for environment, profit, & convenience)
3. Cost
3.1. Magnesium Sulfate (MgSO₄)
3.1.1. Weight: 500g Cost: $78.65
3.1.2. Weight: 2kg Cost: $139.65
3.1.3. Weight: 10kg Cost: $695.00
3.1.4. Best price: 10kg $69.50 per kg
3.2. Calcium Chloride (CaCl₂)
3.2.1. Weight: 1kg Cost: $78.90
3.2.2. Weight: 5kg Cost: $202.50
3.2.3. Best price: 5kg $40.50 per kg
3.3. Magnesium Chloride (MgCl₂)
3.3.1. Weight: 1kg Cost: $63.60
3.3.2. Weight: 5kg Cost: $174.30
3.3.3. Weight: 25kg Cost: $564.50
3.3.4. Best price: 25kg $22.58 per kg
3.4. Iron Powder (Fe)
3.4.1. Weight: 250g Cost: $59.40
3.4.2. Weight: 500g Cost: $80.90
3.4.3. Weight: 1kg Cost: $128.60
3.4.4. Best price: 1kg $128.60 per kg
3.5. Sodium Acetate (CH₃COONa)
3.5.1. Weight: 500g Cost: $282.65
3.5.2. Weight: 2kg Cost: $638.65
3.5.3. Best price: 2kg $319.33 per kg
4. Form of salt (flake, powder, etc.)
4.1. Powder: This form possesses a high surface area to volume ratio, allowing it to dissolve quickly. It would be beneficial for it to dissolve quicker so that it loses less heat to the surroundings so that it reaches a higher peak.
4.2. Flake: Less surface area to volume ratio compared to powder form, thus meaning it would dissolve at a slower rate and also means it wouldn't get as hot as powder form because of this.
5. How fast packs heat up or cool down
5.1. Packs must heat up almost instantly, as if it took extended periods of time, the product would not be as reliable.
5.1.1. How to know if it will heat up quickly or slowly?
5.1.1.1. If the compound has a higher enthalpy change, the temperature will increase at a heightened rate as the compound contains more energy per mole
6. OVERALL PROS AND CONS OF EACH SALT
6.1. Magnesium Sulfate (MgSO₄)
6.1.1. Pros: Relatively cheap at $0.34 required per heat pack Can be sourced and disposed of sustainably High change in enthalpy allowing for fast heat transfer Cons: May be a little more difficult to store
6.2. Calcium Chloride (CaCl₂)
6.2.1. Pros: 2nd cheapest at $0.23 sourced easily Cons: Cannot be sourced or disposed of in a sustainable way
6.3. Magnesium Chloride (MgCl₂)
6.3.1. Pros: Most cost effective at $0.06 worth required per heat pack Cons: Disposal is not extremely safe for the environment
6.4. Iron Powder (Fe)
6.4.1. Pros: Not much weight required Cons Redundant as it is immicible in water, rendering it useless for a change in temperature, disqualifying it.
6.5. Sodium Acetate (CH₃COONa)
6.5.1. Pros: Environmentally friendly Can reuse heat packs containing it Cons: Requires a lot of mass Expensive
7. Sustainability
7.1. Is it safely disposable (in small amounts) without causing harm to the environment?
7.1.1. Magnesium Sulfate (MgSO₄)
7.1.1.1. yes
7.1.2. Calcium Chloride (CaCl₂)
7.1.2.1. no
7.1.3. Magnesium Chloride (MgCl₂)
7.1.3.1. no
7.1.4. Iron Powder (Fe)
7.1.4.1. yes
7.1.5. Sodium Acetate (CH₃COONa)
7.1.5.1. yes
7.2. Can it be sourced sustainably?
7.2.1. Magnesium Sulfate (MgSO₄)
7.2.1.1. yes
7.2.2. Calcium Chloride (CaCl₂)
7.2.2.1. no
7.2.3. Magnesium Chloride (MgCl₂)
7.2.3.1. yes
7.2.4. Iron Powder (Fe)
7.2.4.1. yes
7.2.5. Sodium Acetate (CH₃COONa)
7.2.5.1. yes
8. Miscibility
8.1. Must dissolve in water to be able to produce heat
8.1.1. Is it miscible in water?
8.1.1.1. Magnesium Sulfate (MgSO₄)
8.1.1.1.1. yes
8.1.1.2. Calcium Chloride (CaCl₂)
8.1.1.2.1. yes
8.1.1.3. Magnesium Chloride (MgCl₂)
8.1.1.3.1. yes
8.1.1.4. Iron Powder (Fe)
8.1.1.4.1. no
8.1.1.5. Sodium Acetate (CH₃COONa)
8.1.1.5.1. yes
9. Storage
9.1. Magnesium Sulfate (MgSO₄)
9.1.1. Store in a cool, dry and well ventilated space to avoid moisture.
9.1.1.1. Can this therefore be safe to use in a heat pack?
9.1.1.1.1. Prone to moisture absorbtion, but still safe
9.2. Calcium Chloride (CaCl₂)
9.2.1. Store in a cool, dry and well ventilated space to avoid moisture.
9.2.1.1. Can this therefore be safe to use in a heat pack?
9.2.1.1.1. Prone to moisture absorbtion, but still safe
9.3. Magnesium Chloride (MgCl₂)
9.3.1. Store in a cool, dry and well ventilated space to avoid moisture.
9.3.1.1. Can this therefore be safe to use in a heat pack?
9.3.1.1.1. Prone to moisture absorbtion, but still safe
9.4. Iron Powder (Fe)
9.4.1. Avoid exposure to sunlight and store at room temperature.
9.4.1.1. Can this therefore be safe to use in a heat pack?
9.4.1.1.1. Very safe
9.5. Sodium Acetate (CH₃COONa)
9.5.1. Store in a cool, dry and well ventilated space to avoid moisture.
9.5.1.1. Can this therefore be safe to use in a heat pack?
9.5.1.1.1. Very safe
10. Comfortability
10.1. Must reach an appropriate temperature (In this case, 20 degree increase in 50mL of water)
10.1.1. If the correct temperature is not reached, the user may experience discomfort if the temperature is too high or low
11. Accessibility
11.1. Are the salts and therefore packs easily accessible?
11.1.1. Magnesium Sulfate (MgSO₄)
11.1.1.1. yes
11.1.2. Calcium Chloride (CaCl₂)
11.1.2.1. yes
11.1.3. Magnesium Chloride (MgCl₂)
11.1.3.1. yes
11.1.4. Iron Powder (Fe)
11.1.4.1. yes
11.1.5. Sodium Acetate (CH₃COONa)
11.1.5.1. yes
11.2. Do the salts require extended effort to acquire?
11.2.1. Magnesium Sulfate (MgSO₄)
11.2.1.1. no
11.2.2. Calcium Chloride (CaCl₂)
11.2.2.1. no
11.2.3. Magnesium Chloride (MgCl₂)
11.2.3.1. no
11.2.4. Iron Powder (Fe)
11.2.4.1. no
11.2.5. Sodium Acetate (CH₃COONa)
11.2.5.1. no
12. How much mass is needed to acquire a 20 degree increase in 50mL of water?
12.1. Magnesium Sulfate (MgSO₄)
12.1.1. ΔH=Q/n n=Q/ΔH
12.1.1.1. n=4.18/84.85 =0.04926340601 mol ≈0.0493 mol
12.1.1.1.1. n=m/M m=nM =0.0493*120.38 ≈5.93g
12.1.2. M = 24.31 + 32.07 + 4(16) ≈ 120.38g/mol
12.2. Calcium Chloride (CaCl₂)
12.2.1. ΔH=Q/n n=Q/ΔH
12.2.1.1. n=4.18/82.8 =0.05048309178 mol ≈0.0505 mol
12.2.1.1.1. n=m/M m=nM =0.05054*110.98 ≈5.61g
12.2.2. M = 40.08 + 2(35.45) ≈ 110.98g/mol
12.3. Magnesium Chloride (MgCl₂)
12.3.1. ΔH=Q/n n=Q/ΔH
12.3.1.1. n=4.18/155 =0.02696774193 mol ≈0.0270 mol
12.3.1.1.1. n=m/M m=nM =0.0270*95.21 ≈2.57g
12.3.2. M = 24.31 + 2(35.45) ≈ 95.21g/mol
12.4. Iron Powder (Fe)
12.4.1. ΔH=Q/n n=Q/ΔH
12.4.1.1. n=4.18/824.2 =0.00507158456 mol ≈0.00507 mol
12.4.1.1.1. n=m/M m=nM =0.00507*55.85 ≈0.283g
12.4.2. M ≈ 55.85g/mol
12.5. Sodium Acetate (CH₃COONa)
12.5.1. ΔH=Q/n n=Q/ΔH
12.5.1.1. n=4.18/17.32 =0.24133949191 mol ≈0.241 mol
12.5.1.1.1. n=m/M m=nM =0.241*82.03 ≈19.77g
12.5.2. M = 2(12.01) + 3(1.008) + 2(16) + 22.99 ≈ 82.03g/mol
12.6. Equations
12.6.1. Q: (constant for all above equations) Q=m*C*ΔT Q=50*4.18*20 Q=4180J /1000 Q=4.18kJ
12.6.1.1. Number of moles formula: ΔH=Q/n n=Q/ΔH n=?
12.6.1.2. Change in enthalpy of each compound MgSO₄: ΔH ≈ -84.85 kJ/mol CaCl₂: ΔH ≈ -82.8 kJ/mol MgCl₂: ΔH ≈ -155 kJ/mol Fe: ΔH ≈ -824.2 kJ/mol (when oxidising) CH₃COONa: ΔH ≈ -17.32 kJ/mol
13. Therefore, which salt is theoretically the best to use for a heat pack/which salts are we going to test?
13.1. Sodium Acetate: Despite the immensely increased cost compared to other salts, it can be used in reusable heat packs, allowing for a vastly increased sales cost, it is environmentally friendly, and is very safe to use in heat packs.
13.1.1. With the mass of 19.85g, we will not use that amount, as it will be too costly for the experiment. We will be required to extrapolate the data based on the small mass we instead use (~5g)
13.2. Magnesium Sulfate: Remains very environmentally friendly. While having a relatively high cost, ($0.34/p) the high increase in sustainability compared to a salt such as magnesium chloride makes up for the slight loss in profit. Safe to use in heat packs (will not absorb water prematurely, will not corrode, etc.) High change in enthalpy allowing for fast heat transfer (ΔH ≈ -104 kJ/mol)
13.3. Calcium Chloride: Easily sourced, however not sustainable Costs only $0.23/pack
13.3.1. Magnesium Chloride would have been used if it was available to test as it is extremely cheap, and also has the highest theoretical enthalpy value.
14. Cost needed for a single heat pack
14.1. Magnesium Sulfate (MgSO₄)
14.1.1. Mass required 4.84g Cost per Kg $69.50 69.50/1000 $0.0695 per gram *4.84 ≈ $0.34
14.2. Calcium Chloride (CaCl₂)
14.2.1. Mass required 5.70g Cost per Kg $40.50 40.50/1000 $0.0405 per gram *5.70 ≈ $0.23
14.3. Magnesium Chloride (MgCl₂)
14.3.1. Mass required 2.57g Cost per Kg $22.58 22.58/1000 $0.02258 per gram *2.57 ≈ $0.06
14.4. Iron Powder (Fe)
14.4.1. Mass required 0.283g Cost per Kg $128.60 128.60/1000 $0.1286 per gram *0.283 ≈ $0.04
14.5. Sodium Acetate (CH₃COONa)
14.5.1. Mass required 19.85g Cost per Kg $319.33 319.33/1000 $0.31933 per gram *19.85 ≈ $6.34